This hentai didn't make sense compared to the game. Teacher just goes crazy after years in the school? It was set up that the glasses chick was being bullied in class so you'd expect crazed teacher might have some sorta of relation to the glasses girl such as maybe a family member. So he snaps and goes on a tirade of madness via his "Special lesson" but nope didn't make much sense. Then again everything in the anime was instigated by the students. The teacher was bat shit crazy but interesting enough he didn't say anything specific, for instance what he whispered in the kids ear was "do as you see fit". The only thing a bout this that made any sense was that it parodied lord of the flies on what happened when society breaks down.