After her husband died while their son Manabu was still young, mother and son lived alone together. As his twentieth birthday approaches, his resemblance to his father brings her both maternal pride and a woman's bittersweet longing. On the night he turns twenty, they share his first alcoholic drink. She drinks more than usual, and the equally tipsy Manabu becomes unusually affectionate, drawing mother and adult son toward a forbidden night together that leaves her overwhelmed and squirting.