At a house party celebrating her engagement to Seiichi, Ichika meets Horio, her fiancé's longtime best friend. After discovering a weakness he can exploit, Horio repeatedly pressures her into sex and traps her in a cycle of betrayal. The more she resists, the more excited he becomes. He even proposes filming them fucking to show Seiichi, turning the couple's once-happy home into a nightmare of coercion and infidelity.