Could be a unknown character, despite contradicting the probability that he hasn't built a meaningful relationship with people other than the females he's shown to have interacted with at that school, due to his face thing. Everyone here and their mother theorized it was the sensei before the 2nd chapter dropped, I feel like there's no way Jap. readers and editor/author wouldn't also feel the same while doing the initial manuscript - so its possible we're being baited. But then again predictable as hell manga plot developments are nothing new.