@Etits The closest one that comes to my mind is Higanjima. The English translation is very far behind the Japanese and Vietnamese version (not sure about the others), but if you haven't read it yet, now is a good time to start.
Also look for Terra Formars, Drifting Classroom, Tenkuu Shinpan, Hakaijuu. There's a few more I've read a long time ago, but these came to my mind first. Check them out if you haven't already.
Oh, dear. Just like James A. Janisse from the Kill Count, I don't count the death until I see the body.
Hasegawa is the monkey's ally, isn't he? This isn't the sort of comic where a named character dies offscreen without so much as a glimpse of before the kill happens. It's gotta be him.