I have limited information, but I figured someone may be able to help.

I'm looking for a manga I read a while back but forgot the name. It's from before 2013 I think.

A school girl (a class president maybe?) confronts a male class delinquent due to his constant misbehavior. The delinquent suggests a (sex?) contest, and if she can resist his skills, she will win.

The first sex scene between them is in the classroom. Over the next few chapters he slowly "mind breaks" her. The last scene of the entire story is of him revealing to the reader that she is broken, and she's locked in a room in full bdsm outfit (ball gag, vibrators taped to nipples, vibrating dildo, etc.) and forced to constantly orgasm. The series was definitely not comedic or cutesy.

Any help is appreciated.

it might be this: https://www.mangaupdates.com/series.html?id=6634
It has also anime by the same name