I know that this is the way it is shown, it seemingly makes sense as described. I just think it wouldn't make sense for a human being. Elementary school kids are not usually that cognisant of those kinds of changes. You just enter a new friend group, you adapt, sometimes you change, and sometimes you don't. If you don't, you go back to being "yourself" when you are not with other people.
But if years later you are still affected, that means you just changed. I don't understand why he has to put on that specific "kind person" mask, seemingly despite himself. That just doesn't feel like how humans work to me. At the same time, he claims he didn't care about Miyu all that much when the only reason I can see him still being affected is that her death was deeply traumatizing.
In my eyes, it paints him as either not making any sense as a character, or as an unreliable narrator, even within his internal monologue.
