Haruo and his wife lived together out of concern for his mother-in-law Fumiko, who had been left alone after her husband passed away. Fumiko was grateful to her daughter and son-in-law and had built a good relationship with them, but one day, their relationship changed when Haruo accidentally saw Fumiko indulging in masturbation. Fumiko's seductive and lewd behavior never left Haruo's mind. In fact, just seeing Fumiko reminded him of her lewd behavior, and he could no longer contain his excitement. Finally, Haruo could no longer bear it any longer...