I have a feeling that he didn't kill those guys because he "felt like killing someone" or whatever he said.
I think those guys did something to Sophie (she was basically naked in the flashback)
and grant probable lost his mind
but he didn't want to admit that he cared for Sophie so he lied.
He literally casually murders a guy because training with him isn't fun anymore. The fact that he needed to die is irrelevant to the fact that he killed him with no remorse.
However, if you want to address the thing with Sophie, she's a prostitute, so being naked isn't surprising. She just walked out of her room, and she had no injuries.
I didn't say they "hurt" her.
Maybe them having sex with her was enough to piss him off.
but yeah I agree with you, Grant is the most compassionate character in the manga
P.S. I don't consider the emotionless enhance humans as people they're just bioweapons in my eyes (it's not like its going to hurt their feelings anyway... cause they have none (￣∇￣"))
A dude who casually murders people ended up being one of the most compassionate characters in the story.