This shit is treating this random rapist asshole like he's got dirt on them he can blackmail them with or is a fucking prince or something. He has no reason to follow him out to an isolated spot, no reason to take even a single punch from him, and no reason one of them couldn't just whip out a phone and record the whole thing. Maybe you don't have enough evidence to get the guy on attempted rape, but record him making an unprovoked attack on a minor in cold blood? While I'm not an expert on Japanese law I can't see that as anything but a direct ticket to jail.
What is the purpose of this scene? Drama? To lead into the confession? Just an excuse to have the asshole get kicked in the balls? Was there really no way to accomplish any of that without making your "cool edgy" archetype character look like a half-witted doormat and his good boy friend like some loser who stands by and does nothing?