In the shadowed halls of the Sagemiya household, twin siblings Misaki and Shun battle an inherited curse that awakens forbidden desires between blood relatives. Determined to resist these impulses, they cling to their resolve and keep their distance. Yet Shun’s composure finally breaks, leading him to seek solace from their elder sister Kagu. When Misaki learns of the encounter, her own defenses begin to crumble, drawing her toward Shun in turn.