
And the truth is she already knows what he’s capable of in full. Makoto is highly suspicious of everyone and doesn’t want anyone…even his own mother getting in his way. He realized she not only knew how to get into his computer but looked at his search history. It’s a careful line she’s walking and her efforts paid off, he now only thinks in explicit detail about killing others that bother him. He’s having some real complicated emotions and thoughts…juggling feeling immensely gratified with killing not only another human but someone he’s realized he loves now and feeling wretched and empty for doing so.
I wonder if an alternate version now that she changed the course of event would be still going through with his dangerous games, but she prevents him from actually killing anyone. Or less people from her intervention.

Read on if you don't mind a spoiler babe
(づ ̄ ³ ̄)づ
You hit it dead on (pun intended lol) as of now, he has thoughts of killing her but just the idea of it makes him sick to his stomach. And so he realizes he actually fell in love with her. However, he still wants to kill her cuz he's truly fcking crazy but also he can't cuz y'know he's in love with her, he doesn't want her to be gone. That love prevents him from killing anyone else cuz he wants his first kill to be special. It has to be her, it's romantic in a fcked up way lol

I figured as much…I’m glad she saved his classmates but at what cost? But his psyche is twisted or fucked up. I kept thinking about the line between brilliance and insanity being a thin one. He’s a genius but ever since he was small only taking life has given him a thrill. I like that the author made the soul match the the FL character, since she’s isekaied her personality and behavior is different. I don’t think his original stepsister would have made a fool of herself to make him actually confused about her human behavior and wonder what she’ll do next.
Ma boi, Iwai, I know you're in love with her and concerned but honestly, bringing up something from 2nd grade isn't proof enough. You nailed it but MC can easily deny cuz her nii-chan truly has been harmless to people so far. There's a reason people flock to him and it's because he's good in pretending and acting nice despite being a psychopath. Plus, she's doing her best to keep him being "kind" so saying he isn't surely terrifies her. It's unintentional but that will definitely not endear you to her.