after all the sensitive shit, why would he sleep with her, the grabbing of the hand was also done for that reason, the bath I get it as it was "forced" by the card.
also MC wasn't a good person at least for his friend, as he's probably with a concussion from an ashtray, like wtf hahaha, and also probably made them break up, another reason to made the sister hate him.
sidenote: MC was clever even if he was a good person, so it feels cheap that from time to time, he would act stupid to make Rikai better or to make it easier to solve the case. (ex. him not realizing vice prez likes him). Also how he defeat her on the game, was what he wanted to do again so it's weird making his win an exception in the game.