Although married, Reiko has almost no sexual contact with her husband and grows increasingly frustrated in her daily life. Meanwhile, her stepson, Shinnosuke, has a strong sex drive, and whenever Reiko enters his room, she is aroused by the powerful masculine scent that lingers there, stirring intense emotions within her. One day, she accidentally witnesses him masturbating and, unable to resist the sight of his thick, erect cock, she gives in to his advances and strokes him to climax. However, Shinnosuke quickly becomes erect again immediately after ejaculating, proudly displaying his relentless arousal to Reiko. Drawn deeper by his extraordinary stamina, Reiko finds herself increasingly seduced, and a new, forbidden relationship begins to unfold.