Natsuko had been living with her son Masaki since she separated from her husband. One day, she was asked to look after her acquaintance's son Yusuke, and the three of them began living together. Masaki, who had been monopolizing his mother, became interested in Natsuko's large breasts and began to feel Kokoro when Yusuke tried to get cozy with her. When Masaki wasn't looking, Yusuke would get cozy with Natsuko, touch her large breasts, and ask to take a bath together.