NOOOO!!! After reading the first chapter, the MC should’ve let the girl he killed dead instead of reviving her, what a letdown! If he left her to die, this series would’ve automatically be considered unique already, but instead he has to revive her for no apparent reason, just like many other series like this one!
The MC didn't
intend to kill in the first place. The girl's defense was simply way, way, way below his expectation.
Given that he wants to live "normally", it's understandable that he doesn't want to carry the guilt, moral and/or legal, attached to killing someone. Even as self-defense, killing someone is not a light decision for a human with basic morality. Healing her when he had the power to do so is fine, consistent with what we know of his personality.
He has killed a lot of individuals in the other world (whether that includes humans is uncertain), but that was simply how different the values in the other world were. Back as a "normal" youth in a "civilized" society, he doesn't want to stray from the standards of the modern world.
I imagine that his "normal life" is going to be thoroughly stress-tested, as it already is on this first day of school.
Give this man an attempt at normalcy even as his original world turns out more fantastic than he knew.
He has spent 6 years in a medieval-fantasy hell hole, with no modern comfort, little morals and gruesome life-and-death battles against literal demons. He didn't enjoy the experience, so it's more consistent that he wants a normal peaceful school life rather than more fighting and slaughter.
If you want stories about ruthless returners who kill any annoyance on sight, there are such stories too.
This one starts as a pretty balanced one where the MC doesn't let himself be trampled upon, nor does he just kill without qualms. I'll see how long this balance will last.