After separating from her husband, Natsuko began living alone with her son, Masaki. One day, she agrees to take in Yosuke, the son of an acquaintance, and the three start living together. Masaki grows increasingly aware of his mother's large breasts and becomes sensitive to Yosuke's affectionate behavior. Yosuke, taking advantage of Masaki's absence, draws close to Natsuko, touching her breasts and showing growing intimacy. When Yosuke persistently asks to bathe together, Natsuko hesitates, mindful of Masaki's reaction, yet begins to sense a shift in the dynamics between them.