36-year-old Saki remarried a man much older than her and had a new son. Her son Yuki, having grown up in a single-parent household, has a slightly mother-dependent personality. One day, he returns home from school with his girlfriend. Saki brings tea to his room and peeks through the crack in the door, only to witness her son failing at losing his virginity. Later, seeing Yuki depressed, Saki comforts him—and gently begins teaching him how to have sex. "This stays a secret from your father, okay?" The story portrays Saki, a mother whose affection runs deeper than blood, giving herself completely to her son in an intimate, forbidden bond.