@truepurple @blueoddog I don't think it's sudden. It makes sense to me
. I think the change is drastic, but his actions are very real and believable.
You can see he just snapped when Kanami said 'I'm trying really hard, let's get through this together'. Like, the first half of the chapter is basically giving us the brother's POV. You can see he is not willing to accept the backstabbing and selfish 'charity' of his relatives: he's probably the one who had to make all the funeral arrangements, been dealing with phone-calls about the death, writing letters, etc.
You can almost just... see his thought bubble on the page when Kanami says 'I'm trying really hard':
'you're trying really hard? what have you done, you haven't had to do ANYTHING while i've had to grow up and deal with the real world and the lawyers and our shitty relatives. you want to get through this together? i've been dealing with all of this ALONE while you just sit on the floor and cry'.
(reality check: she's a kid she shouldn't have to bear any of that responsibility. but like. the big brother is a kid too, you can see from the school uniform he's still in high school. /he/ shouldn't be bearing this responsibility and burden either. like, there's blame to be dealt here, but the big brother is dealing it onto the wrong person Big Time.)
And.,. yeah. Sometimes when you cross that line, it's so much easier staying across it and never going back. Never apologizing. Not all of us respond to tragedy and trauma in healthy or kind ways. It doesn't excuse any awful actions we commit, and it definitely doesn't excuse us from taking responsibility for those actions, but... I think it's very real and relatable.