Living with his father, Kunio, is his son, Kyo-suke. His mother left home due to Kunio's infidelity. Worried about the situation, her younger sister, Rie, comes over to help with housework. Kyo-suke finds himself drawn to Rie’s innocent and carefree demeanor as she goes about her chores. Noticing his intense gaze, Rie smirks back at him with a knowing smile. That night, Kyo-suke discovers a shocking truth—Rie is actually the woman his father has been cheating with. When Kyo-suke secretly sneaks a peek at their illicit affair, he locks eyes with Rie mid-thrust. In that instant, their relationship takes a sudden, passionate turn.