Hayato Mimura Takuya, Yukio Mimura's cousin, arrives unannounced at the family mansion intent on expelling Yukio and Reika Uehara. He engineers a contest tied to the family’s dark history, reviving a practice their fathers once engaged in, where breaking Reika Uehara determines ownership of the estate. His motives encompass seizing the mansion, claiming the family fortune, and harboring a personal interest in Reika.

Functioning as an antagonist, Hayato leverages the family’s sadomasochistic legacy to enforce his agenda. He actively participates in explicit, coercive acts during the competition, demonstrating his ruthless pursuit of dominance over the property and Reika. His actions propel the central conflict, directly opposing Yukio’s efforts to protect Reika and retain their home. Hayato’s role remains singularly focused on initiating and sustaining the contest for control of the mansion.