Kinbaku no Yakata: Ryakudatsu 1

Mimura Yukio came from a wealthy family and never wanted for anything. Kind and gentle, he obediently fulfills his dying father's final request: find a previously unknown cousin and allow him to live in the family mansion. But his cousin Hayato has other ideas for the family's mansion, its fortune, and especially Yukio's girlfriend Reika...

Woefully unaware of his family's sadomasochistic history, Yukio is forced to agree to a sexual competition to avoid the exposure of the family's dark secrets. A competition where Reika has become the playing field: the first to break her (as one would break a horse) is the one who gets both the mansion and the money.