I was already pretty into vice-prez, but this. A surprise, to be sure, but a welcome one. Full on BDSM isn't really my thing, but the spanking and the demure attitude? Noice.
The guy gets credit for taking a more manly approach to this sort of thing than the vast majority of romcom/harem MCs would, but I think that he wasn't hard enough--Yuuhiin got off way too easy.
Haruta should have closed his hand before the swing.
Though he should teach her what incurring the wrath of a man means (most women IRL think it means nothing, particularly because of that chivalric rule they exploit forbidding violence against a woman), it'd be a strategically unsound move. That snobbish whore wouldn't take that loss of face lightly, and would probably attempt to retaliate with her family name. Perhaps a harder slap, but definitely a disclosure of the day's events to Mone-san.
He did what he did, and it should have been a clear message, but Yuuhiin only apologized in what she considered a nightmare, effectively to no one at all. She woke up aroused--this guy slapping her in the face was nothing more than a lovetap to her. She learned nothing, and I wouldn't be surprised if this was just a prelude to more flagrant disrespect to both Haruta and Mone-san--her apparent "good will" on that one page be damned. Speaking of which, imagine a guy sexually molesting and blackmailing another guy's girlfriend just to make that second guy and his girl a "man and woman". He would deserve to get more than just his jaw broken.
These were easily the worst three chapters of the manga so far. I hope the author doesn't tread this sort of path again.