Hayato Mimura appears unannounced at the family mansion, demanding immediate evacuation from occupants Yukio Mimura and Reika Uehara. He claims the estate as a previously unknown cousin, leveraging a dying wish from Yukio's father instructing Yukio to find him and grant residence.

To settle the ownership dispute, Hayato proposes a contest mirroring their fathers' method for determining inheritance: "breaking" Reika Uehara. The first cousin to psychologically and physically dominate her wins permanent rights to the mansion and its fortune. He orchestrates this confrontation, aware of the family's concealed sadomasochistic traditions, and coerces participation by threatening to expose these dark secrets.

Hayato's motivations focus on seizing the estate's material wealth and asserting control over Reika, whom he views as an object to be claimed alongside the property. His actions consistently initiate conflict, driven by greed and the desire to displace his relatives. He exhibits no significant evolution or redeeming qualities, remaining solely focused on winning through Reika's subjugation.

The narrative positions him as the antagonist whose manipulation forces the central struggle. He exploits generational trauma and hidden familial practices for personal gain. His background prior to arriving at the mansion remains unexplored beyond his sudden emergence as an inheritance claimant.