Such a well-written tragedy and series of characters. Narumari has already crossed the moral event horizon and can't turn back after he was pressured to participate in a gang rape, and so feels that he must justify his deeds to himself by getting the girl he loves, only for it to go south because he can't properly communicate with her. If you notice, it's heavily implied he's suicidal as he's standing on a bridge and riding a motorcycle AGAINST the flow of traffic.
What makes this more ironically tragic? Hiroshi isn't even aware of Narumari's existence, and only just NOW started having implied feelings for Kanae. Hiroshi is unable to communicate with anyone, and so he ends up committing horrible atrocities and deeds. There's a million minor ways all of this could have been avoided, and yet it wasn't. It's very Shakespearean in a sense and it works very well as a character study, with all characters having motivations and justifications that are internally consistent with themselves, and as a story about the world falling to pieces without the person who it is happening to ever realizing it...