Shirou is 'used to seeing dead bodies' precisely from the Fire that occurred after the 4th Grail War. The line was meant to be another reminder of his mindset and what drives him.
Edit: Also, rip Best Fate Waifu.
Rohit Nair
2019-02-26 03:18:00 +0000 UTC
When the fake assassin was summoned by caster, she basically took the spot from a master who could have summoned a proper assassin servant.