Ryo, a stepmother living with her daughter and son-in-law. She no longer feels lonely after living alone due to her husband's transfer, but her body is throbbing with desire and her sexual desire is growing. Then she finds out that her son-in-law, Taro, has a huge penis... Taking advantage of the fact that her daughter and son-in-law are sexless, Ryo approaches him, saying, "I'll take your daughter's place..." and indulges in her carnal desires. Ryo invites him wherever she goes and enjoys his huge penis to her heart's content. Taro, swept away by the pleasure, begins to become addicted to his stepmother's seductive body and desires it himself...