Nobody wants anybody to get hurt. It's mostly that.
Also, the last childhood friend finally appeared since they all are named after the days of the week.
More like a final boss. Yakuza princess that kidnaps Eiyuu right when he was making a choice between the harem, one of them or none of them. The yakuza girl had Eiyuu as a rival at the same elementary school that him, Akari and Shio went but none of the 3 remembers her. And of course he made a stupid promise to marry as kids. But she just wants to use him as an excuse to not go to an arranged marriage so he'll have to pretend for a while to be her fiancée. We all know how this will turn out.
But I think the 5 girls will have to save him somehow. And yeah, the sensei was already completely rejected.