Due to his strict upbringing by his biological father, Taichi grew up with a dark personality. Yayoi, who married Taichi's father five years ago and became his stepmother, has long observed his suffering and agonized over how she could help him. One day, after catching Taichi masturbating, Yayoi resolves to engage with him sexually. For Yayoi, Taichi—close to her in age—becomes a more essential presence than her husband. One day, she plans a trip with Taichi alone, intending for this journey to mark the end of their relationship. However, during this trip, her feelings begin to waver...