1-5

Chapter 1: I’m Done Being Human! 

Buzz!!! 

A piercing roar of an accelerating engine cut through the air as a massive truck barreled toward pedestrians walking with their heads down on the sidewalk. 

“Ahhh!!!” 

The screams of those around him snapped Riku out of his phone-induced trance, but it was already too late. By the time he looked up, the truck was practically on top of him. He could even make out the dents and scratches on its hood, along with faint traces of crimson blood. 

“Is this thing a seasoned actor?” Riku thought, his mind inexplicably flashing to the classic “isekai truck” trope. The déjà vu was almost too perfect! 

Boom!!! 

The collision sent Riku’s body flying like a kite with its string cut. The truck had singled him out as its sole unlucky target. 

In his final moments, Riku clearly saw the green light flashing on the traffic signal. He definitely hadn’t run a red light! 

Cough, cough, cough!!! 

Riku jolted upright, his chest heaving as he gasped for air, his eyes bloodshot as if he’d just died and come back.  

“No, wait—I did die once already.” 

Looking around, his heart was a mess of emotions. The distinctly Japanese-style buildings, with their blend of traditional wafu and Tang dynasty influences, were nothing like his everyday life. There’s no way that truck could’ve sent him crashing all the way to a neighboring island nation, right?  

And the temperature was off—much colder than before the accident. His thin autumn clothes felt woefully inadequate. 

Clearly, with the “help” of that truck, he’d been isekai’d. 

Hiss~~~ 

Riku clenched his teeth, sucking in a sharp breath, making a tiny contribution to this world’s global warming.  

“All those times I joked online about when it’d be my turn to cross over, and now it actually happened.” 

He muttered a self-deprecating quip. Luckily, he was the classic isekai protagonist: an orphan raised in an orphanage, no parents, no ties, nothing holding him back. It made sense the “hero” role would fall to someone like him. 

After a bit of self-mocking to ease his nerves, Riku’s first move was to check his body. 

Still wearing his cheap casual clothes, no bloodstains, all limbs intact—no missing arms or legs. Finally, he checked his, ahem, manly attributes.  

A long sigh of relief. Still there, and still just as impressive. 

It seemed he’d crossed over with his physical body intact, not soul-transferred into someone else’s. That was a relief—he didn’t want to live with someone else’s face, and he wasn’t ready to part with his own handsome mug. Who knew what kind of body he’d end up with otherwise? 

“System? Cheat skill? Old mentor? Any gods out there? Anyone home?” 

After checking his body, Riku didn’t rush into action. Having thoroughly studied the Transmigrator’s Essential Guide, he knew the first step was to check for a [System] or some kind of transmigration perk. 

After trying everything he could think of, he gave up. No response. All his efforts were for nothing. 

“No system? Or does it have some kind of activation condition? Don’t tell me it’ll only kick in after I’m already invincible.” 

Grumbling, Riku accepted the reality that he had no [System] to rely on for now. He moved on to step two of the Transmigrator’s Essential Guide. 

“Observe the surroundings and figure out where and when I am.” 

Riku got to his feet and started carefully scanning his environment. 

It was nighttime, the moonlight dim. Streetlights—old-fashioned but electric—lit the area, and power lines ran along the road. That ruled out being in ancient times.  

He was standing by a roadside, leaning against someone’s courtyard wall. The buildings around him had a strong anime aesthetic, all wooden and distinctly old-fashioned. 

No skyscrapers in sight, and the architecture didn’t scream modern. That left the possibility of being in the recent past. 

After some quick deduction, Riku concluded he was likely in early modern Japan. The buildings and the kanji on shop signs pointed to that. 

“Now I just need to figure out if this is still my original world or some place crawling with supernatural beings.” 

Riku stretched, loosening his joints. Maybe it was psychosomatic, but his body still ached faintly from the truck impact, leaving him feeling off. 

The streetlights were dim, and the area was deserted. Riku launched into a quick set of radio calisthenics. By the end, his body felt much better, more limber. 

“What are you doing?” 

A voice suddenly spoke from behind him, dripping with curiosity and confusion. Riku nearly jumped out of his skin—how did this guy sneak up so quietly? 

Spinning around, he instinctively struck a military boxing stance, ready to survive “32 stabs and still stand.” But he relaxed slightly when he saw the speaker looked human enough. 

It was a tall, pale young man with black hair and striking crimson eyes, dressed sharply in a Western suit—not traditional Japanese clothing. This further confirmed Riku’s guess about the era; ancient Japan didn’t have Western suits. 

Under the dim streetlight, the handsome young man held a black umbrella, eyeing Riku with a puzzled expression. 

“Bro, it’s the middle of the night—scaring people like that could give someone a heart attack.” 

Riku squinted, not fully dropping his guard. He tried to start a conversation, then realized the guy hadn’t spoken anything. 

But it made sense. He’d already figured this was probably Japan, so running into a Japanese person wasn’t surprising. 

“Foreigner?” 

Before Riku could figure out how to communicate, the young man spoke agai. 

“Yes, That’s awesome! I’m totally lost here and was just wondering who I could ask for help.” 

Riku’s eyes lit up. Meeting someone friendly right off the bat lowered the difficulty significantly.  

“Hey, I’m a tourist . Got separated from my friends and kinda lost. Do you know where this is? And, uh, what’s the exact time?” 

Riku stepped closer, feeling a bit more at ease. The guy spoke friendly—surely he couldn’t be some kind of demon or monster, right?  

What, did Japanese yokai have to learn foreign languages now? Was the supernatural world that competitive? 

“Interesting. Foreigner, huh? Maybe I should’ve tried that sooner.” 

The young man smirked, his smile carrying an eerie charm. Instead of answering, he muttered to himself. 

Riku had no clue what he was talking about. His “Japanese teachers” had only taught him a handful of phrases like “yamete” or “iku iku”—hardly enough for casual conversation. 

“What do you mean?.” 

Riku felt a pang of disappointment, assuming the guy hadn’t understood him. 

“Thanks anyway. I’ll go ask someone else.” 

As a civilized person from modern era—and since the guy had already pegged him as such—Riku politely said goodbye, even if the other party might not understand. Manners never hurt, right? 

He turned to leave, but his face froze, eyes widening involuntarily. 

A sharp, searing pain erupted in his chest, rivaling the agony of being hit by the truck earlier. 

Looking down, he saw a grotesque spike made of flesh protruding from his chest, dripping with blood. The tip wriggled unnaturally, sending chills down his spine. 

Cough! 

Blood surged up his throat, and Riku coughed violently. The specter of death loomed again. The spike seemed alive, splitting into countless smaller tendrils that burrowed into his organs. Pain flooded his entire body. 

“Arghhh!!!” 

Unable to bear it, Riku screamed in agony. He reached for the spike, desperate to pull himself free, but his hands were pierced through in an instant. The spike seemed to grow angrier, writhing more violently. 

It slowly lifted him into the air. Gravity made the pain unbearable, and the more he struggled, the worse it got. 

Born in modern peaceful era , Riku had faced hardships as an orphan but nothing like this. Gritting his teeth, he turned to face his attacker. 

Under the dim yellow streetlight, the young man in a top hat still wore a faint smile. His crimson eyes glinted with a bloodthirsty glow. The flesh spike extended from one of his fingers. 

“Why… what are you?” 

In excruciating pain, Riku forced the words out, his face contorted, speech slurring.  

He’d just died by truck and crossed over, only to face death again before he could even get his bearings. He wasn’t ready to go—not without answers. 

“I’m giving you power. Feel it.” 

The eerily handsome young man spoke slowly. He understood and spoke it fluently. 

Riku’s eyes widened, but his vision blurred as blood poured from his chest. In his haze, the young man’s image began to overlap with a character he’d seen in an anime long ago. 

Buzz!!! 

Before he could confirm the man’s identity, a terrifying surge of blood energy rushed to his brain. His eyes turned crimson, his mind no longer his own. His body began to change grotesquely. 

Horns sprouted from his forehead, a scarlet vertical eye split open between them. His mouth tore into a wide, manic grin, revealing sharp, predatory teeth. His nails blackened and sharpened, his skin paled to a ghostly white, and strange black patterns spread across his body and face. His muscles bulged unnaturally. 

Riku now looked like a demon straight from hell, devoid of any human aura. 

Plop. 

The flesh spike withdrew, and Riku dropped to the ground. His wounds had completely healed, but his mind was a foggy mess, his memories like sludge. 

“This guy’s talent is that bad?” 

The young man frowned, visibly disappointed with the dazed figure before him. 

“Whatever. It’ll do.” 

After a moment’s hesitation, he decided not to retract his blood. This was just a whim, after all. 

“Your mission is to return and find the Blue Higanbana.” 

He walked past Riku, leaving the task behind without waiting for a response. A failure like this wasn’t worth his time. 

“Yes.” 

Riku answered dully, his mind still a haze, his memories distorted and unreal. 

He didn’t know why he had to obey, but the young man’s voice carried an almost magical compulsion, a command that resonated from the depths of his soul. 

This foggy state persisted until a sudden Ding! snapped him awake. 

Ding! 

[Limit System: Activated.] 

Chapter 2: The Ultimate System, Activated! 

[Ding!] 

[Ultimate System: Activated.] 

[Initializing...] 

[Detection: Host is under abnormal control status. 

Abnormal control status has been lifted.] 

[Detection: Special ability "Oni." 

Special ability "Oni" has been retained.] 

[Confirming current world. 

Current world: Kimetsu no Yaiba] 

A series of notification sounds rang out, and that invincible, slightly delayed voice was just so satisfying. Riku’s mind snapped back to clarity, breaking free from that foggy, dazed state. 

“Ultimate System?” Riku muttered, calling out to the system the moment he regained his senses. It was a bit late, sure, but it finally showed up. Clearly, this thing had some activation conditions—like a hidden spark waiting to ignite, just like Naruto’s determination to become Hokage. 

The name “Ultimate System” though? What’s that about? Chasing the ultimate limit? Or maybe it’s like, “Deep blue, show me your limits!” Riku chuckled to himself. He could already imagine Naruto shouting something like that while powering up his Rasengan. But jokes aside, this system was way better than those that only activate when you’re already invincible or half-dead from old age. It’s here now, so why complain? No need for a fancy bicycle when you’ve got a system like this! 

With a thought, Riku summoned the Ultimate System’s interface. A sleek, glowing panel popped up—not a physical thing, but something only he could see in his mind, like a ninja’s mental scroll. 

The panel had two tabs: [World] and [Personal]. 

Riku mentally clicked on the [World] tab, and its contents were short and easy to understand, like a mission briefing from the Hidden Leaf Village. 

[World Page] 

[Past Worlds: None.] 

[Current World: Kimetsu no Yaiba.] 

[Traversal: Function on cooldown. Charging in progress, current progress: 5%.] 

“The world of Kimetsu no Yaiba, huh? Pretty popular anime, from what I’ve heard,” Riku said, clicking his tongue. What a coincidence! He hadn’t actually watched Kimetsu no Yaiba, despite it being a massive hit that nearly broke the internet.  

Still, even if you haven’t seen a super popular anime or played a trending game, you’re bound to pick up some stuff about it. Especially the memes. Like, who hasn’t heard of “Scum Boss”? Riku sure had. 

And just like that, it clicked. That guy from earlier? That was Kibutsuji Muzan, the final boss of Kimetsu no Yaiba—a thousand-year-old Oni King. As the Oni King, Muzan could turn humans into oni under his control. One thought from him, and any oni he created could explode into a bloody mess. Talk about a ruthless leader, worse than any Akatsuki member! 

Riku glanced at his hands. His skin was now a sickly pale, like he’d been drained of life. His nails were black and sharp, looking downright toxic. He checked out his body—muscles bulging way bigger than anything he’d ever trained for, covered in eerie black patterns that screamed “otherworldly.” Add in the demonic horns, the vertical eye on his forehead, and the cracked corners of his mouth, and yeah, no doubt about it—Kibutsuji Muzan had turned him into an oni. 

But thanks to the [Ultimate System], Riku had broken free from Muzan’s control. He was no longer a puppet for that Oni King. 

“This system showed up just in time. Saved my life right off the bat,” Riku said, letting out a relieved sigh. He could feel it—no trace of that suffocating control lingered. The system had completely erased Muzan’s influence, like Naruto breaking free from a genjutsu. 

Good news, for sure. Working under “Scum Boss” was a death sentence waiting to happen. Better to quit and go solo, like a rogue ninja carving their own path. 

“Day one of being forced into a shady organization, and the system helps me fire the boss,” Riku quipped, finding humor in the chaos. It’s the kind of attitude you develop when life’s been a grind, and he was a pro at it. 

But then it hit him. “Wait a sec. If I’ve broken free from his control, would Kibutsuji Muzan know?” The thought sent a jolt through him, snapping him out of his mixed emotions. 

Without a second thought, Riku bolted. He had to get out of here. His current appearance—horns, freaky eye, and all—wasn’t exactly street-friendly. If anyone saw him, good luck explaining that. More importantly, his brain had been screaming warnings since he came to. A deep, primal fear of sunlight. He had to find a place to hide. Getting caught in the sun meant death, no question. 

“Figures. Every oni’s got that ‘weak to light’ trait,” Riku muttered as he ran, channeling a bit of Naruto’s snarky commentary style. Everything was happening so fast, and the info overload was real. He needed a safe spot to sort it all out and dig into this [Ultimate System]. 

Under the cover of night, Riku sprinted through the streets and alleys. His body felt stronger—way stronger. He could probably take on ten or eight of his old self without breaking a sweat. Soon, he left the human settlement behind. From what he could tell, it was just a big village or small town. Why the Oni King was even here was a mystery. 

To avoid Muzan, Riku didn’t dare linger in the village. Instead, he headed for the dense forest outside, where a mountain loomed—a perfect hiding spot. 

As he ran, a chill hit him. The air was colder now, and soft white flakes landed on his body. “Snow?” Riku held out his hand, catching a snowflake. It was cool but didn’t bother him. His new oni body could handle this kind of cold, no problem. 

He kept moving until he reached the foot of the mountain. There, he spotted a wooden cabin with lights on. But after glancing at his monstrous appearance, he wisely decided not to bother whoever was inside. More than that, his body was sending him hunger signals, and the enticing scent coming from the cabin—despite no cooking smoke—made it clear what was drawing him in. It was the smell of humans. 

Riku forced himself to turn away and head deeper into the mountain. Soon, he found a small cave, probably some animal’s old den. After checking it out and finding no creatures inside, he ignored the faint stench and settled in. It wasn’t ideal, but it’d do. 

Finally safe, Riku let out a breath and called up the [Ultimate System] again, this time opening the [Personal] tab. 

[Personal Page] 

[Name: Riku] 

[Level: Lv1] 

[Experience: 0/100] 

[Status: Oni] 

[Attributes: 

Strength: 11 + 5 (Oni) 

Agility: 11 + 5 (Oni) 

Constitution: 11 + 5 (Oni) 

Intelligence: 11 

Perception: 10 

Charisma: 15 - 10 (Oni) 

Remaining Attribute Points: 1]  

**[Skills: 

Oni Lv1: Transformed into an oni by the blood of the Oni King. Strength, Agility, Constitution +5, Charisma -10. Grants Blood Demon Art and Altered Constitution status. 

(Altered Constitution:  

• Undying Regeneration: As long as regeneration power remains, you won’t die, even if your head is smashed.  

• Death by Sunlight: Exposure to sunlight turns the body to ash, and sunlight suppresses regeneration.  

• Cannibalistic Urge: Can only consume human flesh and is drawn to its scent. 

Note: Current constitution allows undying status for 32 hours.) 

(Blood Demon Art: Not activated.) 

Remaining Skill Points: 1 

Remaining Skill Optimization Points: 1]** 

Looking over the [Personal] page, Riku got it. This was a classic character panel—levels, experience, six core attributes, skills, and points to assign. It felt like something straight out of a ninja scroll, with stats laid out like a shinobi’s training regimen. 

He quickly pieced together that the system’s attributes used 10 as the human average. Most people hovered around 10, but his Strength, Agility, and Constitution were slightly above average thanks to his regular workouts. Those muscles weren’t just for show! His extra point in Intelligence? Well, he’d always been a quick learner, picking things up faster than most. As for his 15 Charisma? No mystery there—he was just that good-looking, like a certain blonde ninja who could charm a crowd. 

“Ultimate System, add point,” Riku said, focusing on his attributes. Without hesitation, he dumped his spare point into Constitution. The undying status duration jumped from 32 to 34 hours. 

“Yep, 1 point to Constitution adds 2 hours of undying time,” he nodded, confirming his guess. Besides extending his survival, the boost made him feel tougher, like he could take more hits—almost like unlocking a bit of Naruto’s stubborn resilience. 

Next, he turned to his skills. The [Oni] skill was a double-edged kunai. The “Death by Sunlight” and “Cannibalistic Urge” drawbacks were exactly as bad as he’d felt earlier. “This is ridiculous,” he groaned. “Death by sunlight, cannibalistic urges, and a 10-point Charisma hit just for a +5 to Strength, Agility, and Constitution? Did Muzan mean it when he said my oni potential was trash?” 

“Ultimate System, add point!” Refusing to accept defeat, Riku threw his skill point into [Oni]. 

[Oni Lv2: Transformed into an oni by the blood of the Oni King. Strength, Agility, Constitution +6, Charisma -10. Grants Blood Demon Art and Altered Constitution status.] 

The moment the point was added, Riku felt it—his body got stronger, faster, tougher. A +1 to all three physical stats. Not bad for a single point, though he wasn’t exactly thrilled. “One skill point equals three attribute points,” he mused. It wasn’t amazing, but it was something. At least it boosted all three stats at once, instead of something lame like reducing the Charisma penalty from -10 to -9. If it was that stingy, he’d probably ditch upgrading this skill entirely. 

Still, that -10 Charisma stung. His 15-point charm, which could’ve rivaled a young Kakashi’s cool factor, was now down to a measly 5. Below average. For a normal person, [Oni] would tank their Charisma to 0—or worse, negative if they were already unattractive. Makes sense, though—oni eat people, fear sunlight, and look like monsters. Not exactly charming. 

Riku’s eyes landed on the skill optimization point. From the sound of it, this could be his saving grace. The [Oni] drawbacks were pushing his human limits, especially the cannibalistic urge. He really, really didn’t want to eat people. 

“Ultimate System, add point,” he said, hopeful, assigning the optimization point to [Oni]. 

[Optimization Complete. 

“Cannibalistic Urge” changed to “Shared Feast.” 

Shared Feast: In addition to human flesh, you can now consume oni flesh.] 

“…” Riku’s expression froze. 

“What kind of optimization is this?!” he shouted, sounding like Naruto throwing a fit after a failed jutsu. 

Chapter 3: A Tragic Massacre 

Looking at the results of his skill optimization, Riku rubbed his temples. On the bright side, at least he didn’t have to eat humans anymore, right? 

But then again… weren’t oni (ghosts/demons) just humans transformed? 

“Damn it, this is ridiculous!” 

Riku felt his composure crack, but he quickly pulled himself together. If one optimization didn’t fully fix things, he could just keep optimizing! This time, he’d progressed to eating oni. Maybe next time he’d be munching on grass, and the time after that, normal food! 

Besides, oni weren’t exactly human anymore. Every oni he ate was technically a contribution to world harmony! 

This outcome… was barely acceptable. 

“This system is wild, but I’ve gotta figure out how to keep leveling up. Based on my years of gaming experience, leveling up usually means attribute points, skill points, or optimization points.” 

With more skill optimization points, he could eventually iron out the flaws in his [Oni Transformation] skill! 

One of Riku’s strengths was his optimism. People who could find humor in tough times tended to have a resilient streak, and these challenges weren’t enough to stop him. 

Closing the [Personal] interface, Riku switched to the [World] tab to check the recharge progress of his traversal function. 

“Already at 10%?” 

He was surprised. He hadn’t been in this world long, yet the [Traversal] cooldown was already at 10%. That progress bar was moving fast. 

“Looks like the cooldown for this traversal function is pretty short—maybe just a day or two.” 

Without knowing the exact time, Riku could only estimate. He figured he’d been in this world for no more than five hours, and if five hours equaled 10% progress, the full cooldown would take about two days. 

That meant in roughly two days, he could embark on his next journey to another world. 

“For the next two days, my main quest is to survive. Side quest: level up as much as possible, earn skill optimization points, and fix the flaws in [Oni Transformation].” 

Riku set a small goal for himself. Surviving was the priority, especially in his current state—looking like this, staying alive was no small feat. 

As for whether he’d leave in two days, that depended on the situation. At least he’d have an escape route if things got dangerous. 

Right now, Riku was battling hunger. He wasn’t sure how long he could hold out, but he was determined to stick to his principles. 

Glancing at the cave entrance, he saw the snow falling harder, with icy wind howling into the cave. 

“So, this start is pretty hellish, but not that hellish, right?” 

Leaning against the cave wall, Riku gave a wry smile, accepting his reality. 

Amid the hunger, he forced himself to sleep. The physical and mental strain left him exhausted, and he hoped sleep would dull the gnawing hunger. 

He didn’t know how long he slept, but a familiar scent—the same one he’d smelled at the foot of the mountain—jolted him awake. 

“Someone’s here?” 

Riku’s eyes snapped open. At this point, the only thing that could smell this enticing was likely a human. The scent of an oni was completely different. 

Instantly alert, he fought to control the flood of saliva pooling in his mouth. Was this scent too delicious because he was starving? 

Gulp. 

Swallowing hard, Riku’s gaze locked onto the cave entrance. It was daytime now, and the light pouring in was blinding, almost painfully so. 

At the entrance, a boy was cautiously peeking inside. Riku noticed a prominent burn-like scar on his forehead. 

“Could that be Kamado Tanjiro?” 

The moment he saw the boy, Riku’s mind jumped to the protagonist of Demon Slayer: Kimetsu no Yaiba. He was getting used to seeing anime characters in a hyper-realistic, live-action style. 

“Hello? Is anyone in there?” 

Kamado Tanjiro peered into the cave but didn’t step inside, politely calling out first. 

Tanjiro’s nose was extraordinarily sensitive—beyond human comprehension. Passing by, he’d caught a unique scent he’d never smelled before, which led him here. He carried a bamboo basket filled with charcoal, on his way to sell it down the mountain. 

“Sorry, I’m… not in a good state. Could you please not come in?” 

Realizing who was at the entrance, Riku quickly responded. But as he spoke, he paused. Since when could he speak Japanese? 

He hadn’t even noticed that Tanjiro was speaking Japanese because he understood it effortlessly. 

It didn’t take long to figure out why. A [Limit System] capable of world traversal naturally came with a language translation feature—pretty standard stuff. 

“Oh! I’m so sorry for intruding!” 

Hearing the response from the “mysterious being” inside, Tanjiro was startled. He apologized immediately and prepared to leave. 

But before he did, he hesitated, turning back to ask, “Do you need any help?” 

Tanjiro was surprised because he hadn’t expected a human inside—the scent was nothing like the human smells he knew. But since it was a human, and they seemed to be in trouble, he wanted to offer assistance. Being stranded on a mountain in this weather wasn’t good. 

“Thanks, but I’m fine. I just need to be alone.” 

The voice from the cave carried a clear hint of wanting the outsider to leave. 

Tanjiro scratched his nose awkwardly. He’d probably disturbed someone resting. If he were woken up by a stranger, he’d feel annoyed too. Responding politely was already generous. 

“I’m really sorry for bothering you. I’ll go now.” 

Bowing toward the cave, Tanjiro hurried off, not wanting to be urged again. 

Riku waited a moment, confirming Tanjiro was gone before letting out a sigh of relief. 

Though he hadn’t watched Demon Slayer, he knew Tanjiro was a professional oni hunter. With Riku drooling like this, if Tanjiro saw him, the demon slayer probably wouldn’t believe any explanations. 

“I’ve gotta hold it together. Once I cross that line, there’s no coming back.” 

Despite his hunger-induced haze, Riku was clear on this. He couldn’t eat people. Absolutely not. Once he started, it’d be a slippery slope. 

If he fell that far, he’d be no different from the oni. Even if he later optimized away the “cannibalism” side effect, the mental shift would be irreversible. 

Fighting the hunger, Riku went back to sleep. It was still daytime, and he couldn’t go outside. Sleep was his only defense against the hunger. 

Falling asleep wasn’t easy. The hunger gnawed at his mind, making him toss and turn—a different kind of torment from physical pain. 

He endured in the cave until sunset. Nearly fainting from hunger, his eyes bloodshot, Riku finally staggered out. 

He knew nightfall didn’t guarantee safety. For other oni, this was prime hunting time. Neither fully human nor accepted by oni, he had to tread carefully even at night. 

Moving through the forest, Riku marveled at its untouched wildness. Having lived in a concrete jungle, he’d never been in a place like this. 

“Are there any animals? I need to level up.” 

Though the [Limit System] hadn’t explained how to gain experience, Riku’s gaming instincts pointed to the classic method: killing monsters. 

But the snow, though lighter than during the day, kept falling. In this weather, animals were unlikely to be out, leaving him no chance to test his theory. 

The moon was faint, nearly invisible, and the forest was silent except for the howling wind and snow. 

Riku wandered alone, his body not cold but his heart heavy. After two or three hours with no results, he felt utterly isolated. 

If he hadn’t marked trees every few steps since leaving the cave, he’d be hopelessly lost in this snowy wilderness. 

“Maybe I should head back…” 

Just as he considered retreating, an overwhelmingly rich scent hit him, nearly knocking him out. 

“This is…” 

Tormented by hunger, Riku instinctively moved toward the scent’s source. 

“Humans…” 

He fought to stay clear-headed, knowing what the scent meant. He’d finally encountered people in the forest. 

But this smell was too potent—far stronger than anything he’d smelled before, almost overflowing. 

Driven by hunger, Riku hurried to the source. Then he understood why the scent was so intense. 

“It’s literally overflowing… even the intestines are spilling out.” 

Before him was the site of a massacre. In a wooden house, a mother, three boys, and two girls—a whole family—lay dead, neatly arranged in death. 

“Wait… one of them might still be alive.” 

Hunger clouded Riku’s judgment, but he noticed one of the older girls was still breathing. 

“I…” 

He wanted to help, to see if she could be saved, but his feet wouldn’t move. His mind screamed at him. 

“Eat! Eat! You’re starving! Don’t you want to level up? Eating them might do it! Go on, eat!” 

A demonic voice whispered in his ear, eroding his fraying nerves. 

Crunch! 

A sharp sound of flesh being bitten snapped him back. Pain cleared his mind slightly. He’d bitten his own arm, hard, blood seeping out. But the wound healed almost instantly. 

“Sorry, I can’t help you. I have to make sure I don’t eat you first. If I stay, I won’t be able to hold back.” 

Seizing his moment of clarity, Riku turned and fled, desperate to escape the intoxicating scent. 

In the wind and snow, following his marked trees, he retraced his steps, biting himself countless times along the way. 

Back in the cave, leaning against the rock wall, Riku panted, his face smeared with blood, now frozen from the cold. 

“But… why do I feel like I’m not as hungry anymore?” 

Staring at his arm, a sudden thought hit him, spiraling out of control. 

“Did I… just find a system glitch?!” 

Chapter 4: If I Said I Did It Out of Kindness, Would You Believe Me? 

On his way back, Riku took a few bites out of himself. Each chomp was hard and deliberate, and naturally, some accidents happened along the way. Like, say, swallowing a few gulps of his own blood or tearing off chunks of his own flesh. Yeah, that actually happened on the road. 

“Could it be…?” Riku swallowed hard, pulling up his [Personal Page] again to check the description of his newly optimized “Kyokushoku” ability. 

Kyokushoku: In addition to human flesh, you can now consume oni flesh. 

Reading it literally, Riku was certain he’d stumbled onto a bug in the system.  

“No, wait, this isn’t a bug—it’s a feature!” he declared, quickly adapting to the situation. If it worked in his favor, it was a feature. If it screwed him over, then it was a bug. Classic ninja logic, like something Naruto would grin about while dodging a trap. 

Crunch. 

Lost in thought, Riku took another bite out of his forearm. He wolfed down the flesh like a starving shinobi, and sure enough, his hunger eased up. He’d already chomped himself too many times on the way back, so now, as he tore off a big chunk and chewed while watching the wound heal, he didn’t even flinch. 

He was getting used to the pain, which was a good thing. The sooner he adapted, the better—because who knew how long he’d have to keep eating himself to survive? If every meal was agony, that’d be torture. Not that it didn’t hurt now, but still. 

“The taste is… bland. Compared to the scent of human flesh, this is like chewing wax,” Riku muttered, giving his review after a few bites. He hadn’t actually eaten human flesh, but just the smell was enough to know it was on a whole different level. The “oni flesh” he was eating? Zero appeal. If it wasn’t for that, he’d have figured out this system “feature” way sooner. 

“Food’s food. No need to complain when you’ve got something to eat,” he said, channeling a bit of Naruto’s grit. Left arm, right arm—he took turns biting until his stomach was full. The only cost? Some pain. 

Sometimes, when he ate slowly, the previous bite’s wound would already heal before he could take another. It was like a perpetual motion machine—regeneration so fast it defied logic. As long as he didn’t push his regeneration to its limit, food wouldn’t be an issue anymore. 

“This system feature? Ten out of ten,” Riku said, grinning. With his hunger satisfied, his mind felt sharp again, like a ninja ready for the next mission. 

He grabbed a handful of snow outside the cave to wash the blood off his face, then prepared to head back to the “crime scene.” He remembered there was a little girl in that family who wasn’t dead yet. He had to check on her. 

To keep himself in check, he’d stuffed himself to the brim this time. Surely that’d stop him from being tempted by all the blood and flesh, right? 

Following his markers, Riku set off again, glancing at the sky. Dawn was still a while away. His earlier trip, plus “dinner time,” took maybe five or six hours. It was probably one or two in the morning—plenty of time for a round trip. 

The snowstorm had calmed down by now. It was already slowing when he’d returned earlier. Following his markers, Riku soon arrived back at the wooden cabin. 

This time, his head was clear, and he noticed something he’d missed before. The cabin wasn’t alone—there was another building nearby, probably a woodshed. This family likely made a living chopping firewood, a simple life like the villagers in the Land of Fire. 

Pushing those details aside, Riku approached the main cabin and stopped at the door. 

Gulp. 

Even stuffed, the scent of human flesh was still mouthwatering, but at least he could control himself now. He looked at the doorway. A girl in a pink kimono lay there, covered in blood, as if she’d been trying to shield an even smaller child beneath her. She’d failed. 

“…” Riku fell silent. In his hunger-fueled haze earlier, his judgment had been off. There were no survivors here. The only “living” thing was an oni—this girl had been turned. 

He peered inside. A mother had desperately tried to protect her children. Another daughter lay dead behind her. The two boys in the family had fought bravely, giving the girl at the door and the youngest child a chance to escape the cabin. 

“Something’s off,” Riku muttered. “No bite marks on the bodies, and one was turned into an oni. Can a regular oni even do that?” He didn’t know if other oni could, but he sure couldn’t turn anyone into an oni. And wouldn’t a typical oni at least take a nibble in a situation like this? 

His expression shifted as the pieces came together, pointing to one answer. “Was this Kibutsuji Muzan’s doing?” he wondered aloud, stepping inside to sniff the air. But the overwhelming scent of human flesh drowned out everything else. His nose wasn’t sharp enough to pick up Muzan’s trace—like trying to sense chakra in a storm. 

“Forget it. Better get out of here,” he decided. Even without proof, he wasn’t taking chances. Better safe than sorry, like dodging an ambush from the Akatsuki. 

But then he paused, looking at the motionless “oni girl” still lying at the door, showing no signs of waking. “What do I do with her?” he muttered, conflicted. “Poor kid. Family slaughtered, turned into an oni… but I can’t just leave her like this. Should I… kill her?” 

As a regular guy from a peaceful modern era, Riku had never killed anyone. Heck, he hadn’t even killed anything bigger than a freshwater fish. Killing someone—or something—felt like a huge leap. But this “oni girl” wasn’t human anymore, right? More like a “humanoid creature.” 

Still, she looked way more human than he did. That made it harder.  

After two seconds of hesitation, it hit him—oni only die to sunlight, and he didn’t exactly have the means to kill one. “Except by eating…” He glanced at the girl, gritting his teeth. No way he could stomach that right now. And even if he could, eating a living target? That was a line he couldn’t cross. 

Hunger made you reckless, but a full stomach made you think too much. If he was still starving, he probably wouldn’t be agonizing over this. 

“I can’t just leave her,” he decided. “Let the sunlight handle it.” 

He rummaged through the cabin and found some sturdy rope. Effortlessly lifting the “oni girl,” he tied her securely to a post in front of the woodshed. No way she’d break free. 

“Sorry, kid. This is the best I can do,” Riku sighed. Hanging her here would keep her from hurting anyone else. Surely, she wouldn’t want to become a monster either. 

“If I get the chance, I’ll avenge you,” he promised. He felt for this family—their bond, their desperate fight to protect each other. As an orphan, Riku envied that kind of connection. It’s why he was going through all this trouble. Living in this remote mountain forest, they must’ve been happy, right? 

With that done, he didn’t linger. Following his markers, he hurried back to the cave. Staying in the cabin might block the sun, but being surrounded by “gourmet food” was too much for his self-control. Plus, the cave felt safer. If someone found him with a pile of bodies, there’d be no explaining that. They’d probably just burn the cabin down and leave him to fry. But in the cave? Good luck moving a whole mountain to get to him. 

By the time he reached the cave, the sky was starting to lighten. Winter days meant early sunrises. 

“What a night,” Riku muttered, leaning against the cave wall. He summed up his haul: discovered a system feature, solved his food problem, and learned that Kibutsuji Muzan might still be lurking nearby. No progress on “how to level up,” though. Not his fault—he hadn’t run into a single living thing, except for an oni he couldn’t kill. 

“Here’s hoping that oni girl gives me some experience when the sun takes her out. I mean, I put in the work, right?” he said, indulging in a bit of fantasy. He didn’t know how the *[Ultimate System]*’s experience worked, but maybe it’d count. 

“Whatever. No point stressing over things I can’t control. No hunger today, so I can’t just sleep the day away. Time to get to work!”  

Pushing the daydreams aside, Riku stood up. He couldn’t go out in the daylight, but that didn’t mean he couldn’t do something in the cave. 

“Alright, let’s do 100 push-ups, 100 sit-ups, 100 squats, and a 10-kilometer run!” He glanced at the cave’s size. “Okay, scratch the run. I’ll do it in place.” 

“Train hard! Keep pushing! Even with a system, you can’t slack on self-improvement!” he said, hyping himself up like Naruto before a big fight. Sure, adding points was great, but getting stronger through sweat and effort? That hit different. Why not have both? 

The sun rose outside, uncaring of anyone’s plans. Riku started his daily training routine in the cave. Of course, with his new oni-level physical stats, this workout was a bit too easy. He’d need to crank up the intensity. 

“Huff… huff… huff…” Riku controlled his breathing, sweating as he pushed himself. He wasn’t a pro athlete, but he loved fitness and had some know-how. 

But his workout was cut short when a familiar scent hit him—someone was near his temporary base. 

“Is that… Kamado Tanjiro?” Riku froze, recognizing the scent. Then he sniffed again and frowned. “And that oni girl?” 

What kind of combo was this? Wasn’t the main character of Kimetsu no Yaiba a demon slayer? He rubbed his temples, digging through his spotty memory of the anime. He wasn’t big on it, so most of what he knew was half-forgotten, like scraps from a mission report. 

“Wait!” He clapped his hands. He’d found something in the memory junk pile. Kamado Tanjiro had a sister who’d been turned into an oni, always with a bamboo muzzle in her mouth! 

“Hello? Is anyone in there?” Tanjiro’s voice called from outside the cave. 

“…” Riku froze in awkward silence. It hit him—the “oni girl” he’d tied up was probably Tanjiro’s sister! 

“Sorry, I’m coming in!” Tanjiro didn’t wait for a reply. He sounded urgent, rushing into the cave with the “oni girl” in tow. 

When Tanjiro stepped inside, Riku finally saw him face-to-face. Sure enough, the girl had a bamboo muzzle in her mouth. 

“Look, if I said your family wasn’t killed by me and I tied up your sister out of kindness, would you believe me?” Riku blurted out, trying to clear the air. He really didn’t want to take the blame for this mess! 

“I believe you,” Tanjiro replied instantly, so straightforward it caught Riku off guard. 

“Uh…” Riku blinked, thrown off. Then he noticed something odd. Tanjiro… didn’t have a weapon? 

“Please, Mr. Oni! Tell me how I can turn my sister back to normal! I’ll do anything—even if it means you eat me!” Tanjiro bowed deeply, his voice raw with sincerity. He’d failed to protect his family, and if his life could save his sister, he’d pay that price without hesitation. 

Chapter 5: You’re Defying Basic Physics! 

“This…” 

Tanjiro Kamado’s wild move left Riku completely stunned. 

No way around it. For Riku, a guy from modern-day who’d only ever “bowed” to God, this habit of dropping to his knees at the slightest thing was seriously hard to wrap his head around. 

Still, considering the limitations of the era and Tanjiro’s reasons for doing it, it wasn’t entirely impossible to understand. 

“Get up and talk, man.” 

Riku sighed, exasperated, quickly reaching out to help the kid to his feet. 

But the moment Riku extended his hand, the “female demon” who’d been trailing behind Tanjiro, looking all dazed and clueless, suddenly sprang into action. 

Nezuko Kamado darted in front of Tanjiro, her face full of anger, clearly ready to protect her brother. 

“Nezuko, it’s okay. He’s not a bad person.” 

Tanjiro hurriedly stood up, pulling his sister behind him, earnestly explaining to the now-demon Nezuko. 

“How do you know I’m not a bad guy?” 

Riku couldn’t help but ask, even though it sounded a bit like he was picking a fight. He was genuinely curious—how could this kid be so sure he wasn’t trouble? 

With the way Riku looked right now, even he wouldn’t have the confidence to call himself a good guy. His charm had been docked ten points, and he didn’t even have a single intact piece of clothing. His pants were barely holding it together, his shirt was in tatters, covered in bloodstains—he looked every bit like a vicious demon. 

“It’s your scent. I can tell by your scent.” 

Tanjiro answered without hesitation, his sincerity practically radiating off him. 

His honesty, though, only left Riku more confused. 

“My nose is really sharp. I can pick up on people’s emotions through their scent. Even though you’ve got a strong smell of blood on you, I know you’re not a bad person.” 

Seeing Riku’s puzzled expression, Tanjiro elaborated further. 

“…” 

Riku was half-convinced, but given Tanjiro’s status as the protagonist, he leaned toward believing him. Not bad, main character. Comes with a built-in ability to sniff out the good guys. 

At this point, Riku pieced it together—Tanjiro Kamado probably hadn’t become a Demon Slayer yet. 

Realizing Tanjiro wasn’t a Demon Slayer yet, Riku relaxed. The threat to his life was off the table for now. 

Fighting a professional Demon Slayer in his current state? Riku had zero confidence in that. Plus, his “transmigration” ability was still on a 25% cooldown, meaning it wouldn’t be ready until at least midnight. He couldn’t even run if he wanted to. 

“Sorry, kid, I’m afraid I can’t help you. As you can see, I’ve got my own problems to deal with.” 

When it came to Tanjiro’s request, Riku genuinely had no way to help. 

He’d only managed to break free from control thanks to his [Limit System], but there was no way this girl, Nezuko Kamado, could replicate what he’d done. 

“But Nezuko, she…” 

Tanjiro’s face fell at Riku’s words. He’d had high hopes for this demon guy. After parting ways with that Demon Slayer named Giyu Tomioka, he’d brought his sister here. 

“You’re wondering why she’s like this, aren’t you?” 

Riku picked up the thread, understanding what Tanjiro meant. This sister of his did seem a bit… out of it. 

“To be honest, I don’t know much about demons myself. Not gonna lie, I only became one a couple of days ago.” 

After mulling it over, Riku decided to be straight with him. He had a soft spot for this sincere, loyal kid. 

“So you’re saying Nezuko might get better in a few days?!” 

Tanjiro jumped to a hopeful conclusion. Even if she couldn’t turn back into a human right away, becoming as clear-headed as this demon guy would be a start! 

“I didn’t say that. Every demon’s probably different. When I first turned, I wasn’t nearly as calm as your sister.” 

Riku had only ever met three demons: Muzan Kibutsuji, himself, and Nezuko Kamado. How could he possibly know the standard process for turning into a demon? And even without thinking too hard, he could tell Nezuko wasn’t following the usual demon transformation route. 

This anime aired stayed super popular, and never got banned, so there’s no way Nezuko Kamado would ever actually eat people! If anything, Riku should be the one asking her for tips—he was still struggling with the whole “eating” issue himself. 

“Well, Nezuko wasn’t always like this either.” 

Tanjiro scratched his head, quickly catching on after Riku’s comment. That Tomioka guy had also said Nezuko was special. 

“Even though I can’t help you, here’s some advice: never give up. As long as you keep pushing forward, you’ll find a way.” 

Riku put on a serious face. Even if he couldn’t help directly, he didn’t mind planting a seed of goodwill. After all, he was dealing with the same problem as Nezuko. If the protagonist squad figured out a solution later, maybe he could piggyback on their success. More friends, more paths, right? 

“Thank you! I’ll never give up. I will find a way to turn Nezuko back into a human!” 

Sure enough, Tanjiro chugged Riku’s motivational chicken soup like it was the last bowl on earth, looking thoroughly inspired. 

“Mr. Demon, can you tell me what happened to my family? Do you know who did this?” 

Turning Nezuko back to normal was one of Tanjiro’s goals, but he had another: avenging his murdered family. 

Yesterday, after selling charcoal, it was already late, and with the snowstorm, Tanjiro stayed the night at old man Saburo’s place at the foot of the mountain. Early this morning, before dawn, he rushed back home, only to find his family’s bodies waiting for him. 

Tanjiro was devastated. He couldn’t understand why this had happened, why misfortune had struck his family. 

In his despair, he discovered Nezuko was still alive, though she’d been hung up at the woodshed door. Cutting her down, Tanjiro didn’t hesitate to carry her down the mountain, clinging to even the slightest hope. 

Then, Nezuko turned into a demon and tried to eat him. As they struggled, a Demon Slayer named Giyu Tomioka showed up. 

The Demon Slayer wanted to kill Nezuko, which Tanjiro couldn’t allow. He fought to protect her, though “fight” was generous—it was more like a one-sided beatdown. The Slayer didn’t even need to move to shrug off Tanjiro’s attacks. 

In the end, the Slayer defeated both Tanjiro and Nezuko but spared them, moved by how they protected each other. He left Tanjiro an address, telling him to find an old man named Sakonji Urokodaki, then left. 

So, coming to terms with everything, Tanjiro returned home with Nezuko and buried his family. 

It was only then, once he’d calmed down, that he noticed Nezuko carried a scent—one that matched the smell of someone he’d encountered in a cave yesterday. 

Thanks to his keen sense of smell, Tanjiro quickly deduced that two beings had been at his home. One scent was overpoweringly pungent, while the other was fainter. The fainter one matched the person he’d smelled in the cave. That demon must’ve come later and was the one who hung Nezuko up. 

“He might know something!” 

That was one reason Tanjiro came here. Of course, he wasn’t reckless. He’d come because of that “scent connection” from yesterday, which earned Riku a “good guy card” in Tanjiro’s book. 

“First off, stop calling me ‘Mr. Demon.’ My name’s Riku. 

Second, by the time I got there, it was already over, so I don’t know exactly what happened. 

But I’ve got a hunch. The demon who did this is probably the same one who turned me into a demon.” 

Riku hadn’t seen it happen, but he had a strong guess—one he was pretty darn sure of. 

“Who is it? What do they look like?!” 

Tanjiro’s eyes lit up at Riku’s words. Just knowing this was enough! 

“It’s the Demon King, Muzan Kibutsuji. A handsome young guy with sickly pale skin, blood-red eyes, medium height, dressed in Western-style clothes.” 

Riku described Muzan Kibutsuji as he remembered him. The description wasn’t super distinctive, but it’d narrow things down. 

“Demon King, Muzan Kibutsuji…” 

Tanjiro muttered the name, committing it to memory. One day, he’d find this Muzan Kibutsuji and avenge his mother and siblings. 

“What’re you planning to do next?” 

Riku asked, tempted to warn the kid not to stick around since Muzan Kibutsuji might still be nearby. But seeing Tanjiro’s “hot-blooded” vibe, he figured it was better to keep quiet. Otherwise, this guy might actually go pick a fight with Muzan. 

For a kid who’d just lost five family members and had his only sister turned into a half-human, half-demon, staying as composed as Tanjiro was already a miracle. Riku couldn’t ask for more. 

“I’m taking Nezuko to Sagiri Mountain. Mr. Tomioka told me to find an old man named Sakonji Urokodaki there.” 

Tanjiro didn’t know Riku was holding back info and openly shared his next steps. 

“Sounds good. Maybe those Demon Slayers can help you out.” 

Riku nodded. Leaving was the best move—no chance of running into Muzan Kibutsuji here. 

As for this Sakonji Urokodaki guy, he was probably Tanjiro’s guide to becoming a Demon Slayer. Riku hadn’t watched the anime, but he knew the tropes of shonen anime like the back of his hand. 

“…” 

Tanjiro looked at Riku, hesitating for a few seconds before gritting his teeth and asking the question that’d been weighing on him. 

“Mr. Riku, what are you going to do?” 

In Tanjiro’s nose, Riku’s scent was very similar to Nezuko’s. That meant Riku had likely just become a demon too—and, like Nezuko, hadn’t eaten anyone. 

“You’re worried I might start eating people, aren’t you?” 

Riku couldn’t help but chuckle. Tanjiro’s sincerity was refreshing, though his attempt at being subtle was a bit awkward, and his expression gave him away. 

“N-No! That’s not what I—” 

Man, the moment Tanjiro tried to lie, his face twisted like he was in more pain than if he’d been stabbed. 

“Relax, I get what you’re worried about. But I’m like your sister—we’re both a bit special.” 

Riku shook his head with a smile, then, right in front of Tanjiro, bit into his own forearm. 

Tanjiro froze, dumbfounded, as Riku chewed on his own flesh. He couldn’t wrap his head around it. 

“As you can see, I’m not like most demons who can only eat human flesh. I can eat demon flesh—even my own.” 

Riku swallowed the chunk of flesh, flashing a grin full of bloody teeth. The sight was so intense it made Nezuko take a step back. 

“Uh… that’s really…” 

Tanjiro racked his brain for a word to describe it, but his limited vocabulary came up empty. 

Riku’s actions blew his mind. He couldn’t imagine the willpower it took for Riku to casually eat his own flesh like that. 

His judgment was spot-on. To avoid eating people, Riku was willing to torment himself, even devouring his own body. 

In that moment, Tanjiro felt like he truly understood the weight of Riku’s earlier words: Never give up, and you’ll find a way. 

But for some reason, Tanjiro couldn’t shake the feeling that something was off about this scene. He couldn’t put his finger on it, but it just felt… wrong. 

Riku could explain the weirdness: it was all a bit too in line with the law of conservation of energy. Eat an arm, it grows back. Eat it again, it grows back. What, was he running on perpetual energy with zero loss? 

Even normal demons needed to eat human flesh to recover quickly from serious injuries. If they didn’t, their regenerative powers would weaken. But Riku’s stunt completely ignored that rule. Tanjiro might not know much, but his gut—honed by life experience—told him something was strange. 

Still, Tanjiro’s reaction was just due to inexperience. Once he saw Nezuko’s “sleeping technique” later, he’d probably stop thinking Riku was the weird one. 

Nezuko, who could go without eating anything, just sleeping, and still be a powerhouse in battle—too scared of sunlight to even claim photosynthesis as an excuse—was the real physics-defying one. 

At least Riku was eating his own flesh, putting something into his body. If you stretched it, you could justify it. 

Maybe his digestive system was just that good, with zero energy loss. Or maybe demon flesh was equivalent to human flesh for him, and eating a chunk of himself gave him way more energy than it took to regenerate it. 

And if that didn’t add up? Well, the [Limit System] was just that broken. Exploiting a system bug not being logical? Totally normal. 

(End of Chapter)