Currently looking for stories where a boy somehow forces a girl who will do anything with anyone, possibly at the same time, to become his and his alone. I have seen several examples here and there; sometimes the girl's into group activities, other times she just has lots of boyfriends. Either way, and regardless of her relationship with the MC beforehand, the MC decides he doesn't like this and uses skill, force or even love to make the girl quit all other men and stay with him alone. Best example I have is an unfortunately untranslated work titled Plain from Umashika's Apron Dress. The hero is childhood friends with a tiny classmate who he discovers one day with a guy. When he confronts her she unabashedly says that she does it with boys who are "nice" to her as thanks and that even if they're just being nice as a cheap way to get some it still feels good. In fury that his sweet childhood friend has been giving herself to so many men for so long, he demands she "service" him until he's fully satisfied, and proceeds to do just about everything anyone's done to her and a few things no one's done, and by the end she declares her intent to quit with other boys because she wants him to be hers alone.