After divorcing, Aki had to leave her son Naoya behind with his father. The night before she moved out, overwhelmed by loneliness, Aki ended up sleeping with Naoya. Since then, the only thing keeping her alive was the one day each year when she could see him. But now, Naoya's father has remarried, and Aki grows anxious—what if his new wife, his stepmother, takes Naoya away from her? Her chest tightens with dread. Finally, the day arrives: the first time she will see Naoya since he gained a stepmother.