Here's a picture featuring Terra from Kingdom Hearts. The idea was suggested by TPoN.
"How about Terra from Kingdom Hearts, instead of getting corrupted by darkness like the villains expected, his body instead ends up absorbing the darkness and making him grow more powerful? And grow in general, though I think it would be fun to focus on his pecs."
A cloaked figure was able to kidnap Terra with the help from a bunch of Heartless. It was easy for them since it was in the middle of the night while he was camping in the middle of a field. He was going back to the academy, but the way over there was too long, so he needed to camp for the night.
Terra was brought to a dark place, filled with withered, blue trees, covered by a cloudy, purple sky. It seemed that he was taken to the Realm of Darkness. Once he woke up, his sight was fuzzy. Before he could recognize anything, he was shot by a piercing ray. The moment he was shot, he lost his breath and fell to his knees.
This ray was shot by the cloaked figure. It was a particular spell that he could use only once. It's able to make anyone fall under the control of darkness no matter how strong their will was. While Terra was gasping for air, the cloaked figure snapped his fingers, summoning a bunch of pureblood Heartless. Terra was able to see them approaching, but couldn't do anything about it, he didn't have enough energy to move.
Suddenly, one of the Heartless lunged into Terra!...But Terra didn't feel anything. He opened his eyes only to see the Heartless deintegrating into a shadowy cloud...which then seemd to be absorbed by Terra's body. After that happened, Terra could feel a rush of energy course through his whole body, which was enough for him to stand up, and summon his Keyblade to fight off all other Heartless.
Seeing this, the Heartless decided to mercilessly lunge towards Terra, who inmediatedly countered them with attacks. The more fragile Heartless were defeated with one hit, leaving dark clouds after being defeated...which also got absorbed by Terra. After defeating a bunch of HEartless, Terra could feel himself totally pumped up, an amount of energy he's never felt before, which made him want to defeat even MORE Heartless.
The cloaked figure was confused at what was going on, Terra was supposed to be easily consumed by the Heartless with his spell, but it seemed that he accidentally made him more powerful...This isn't good for him, he decided to summon even more powerful Heartless and send them off.
Meanwhile, Terra easily sliced through the hordes. The energy flying directly into his body. When he was fighting the bigger Heartless, the cloaked figure could notice something else...not only Terra's energy was being powered up by the darkness, but his body too! Terra became double the size of his regular height, but his muscles were the major difference. He was already pretty fit, being the muscle of his group, but now, his body looked like he could intimidate even the most powerful Invisibles. His shirt has risen up, showing his powerful abs, and his pecs were ballooning up, which made his shirt leave almost nothing to the imagination.
Terra kept on fighting and growing, sometimes frowining as if something was bothering him. Until finally, he decided to get rid of what was bothering him...his lower clothes! He grabbed him and ripped them off with ease, revealing his thick, powerful legs. They looked strong enough to crush a bunch of Shadows between the two trunks.
The cloaked figure desperately kept on summoning more HEartless...Darkballs, Neo Shadows, Invisibles...even Darksides! but no...all they did was only make Terra more powerful and even MORE massive.
Terra became so big, that it was easier to crush shadows with his barehands. He became so big that Darkside didn't even reach his knees, him being able to easily grab them and crushing them with his hands, absorbing the rich, dark energy from each defeated opponent. Meanwhile, all the other smaller Heartless units were easily squashed under Terra's gigantic soles.
The cloaked figure was already running out of energy...the only option was to escape at this point, but Terra was able to spot him while escaping...will the cloaked figure be able to run away from the growing hero? Who knows. haha
Hope you like it hehe