After divorcing her husband, Mariko raises her two sons, Akira and Shinji. Shinji lives with his father, but during a rare family gathering, the reunited household enjoys a warm and joyful time together. However, following the divorce, Mariko struggles with unfulfilled desires and becomes increasingly drawn to Shinji as he matures into a man—eventually giving in and crossing a forbidden line. Her actions ripple through the family, deeply affecting Akira as well, pulling all three into a taboo relationship. As familial bonds clash with raw desire, their lives spiral into an escalating web of secrets and passion.