Aoya doesn’t seem like a purely impulsive killer to me. He’s been planning this out for 2 years now. There’s definitely some bigger reason he’s killing all these people, but it’s hard to guess at at this point. This manga is a lot of fun.
This manga is a lot of fun! My thoughts are thinking that after he tried to kill himself, he found his perfect prey: Tokiko. He might have been dismembering the bodies as practice for Tokiko too. As for cannibalism, I don't think I'm going to go that far with the idea but it is possible as he sees himself as a monster.