The daughter-in-law's mother, who came from Akita to Tokyo, secretly had sex with her mother-in-law until she ran out of sperm, hiding it from his pregnant wife. (Kiryu Tamaki, OFKU-239)

Because her daughter, who was about to give birth, was hospitalized, the mother-in-law, who had come to the capital to help with household chores, found herself alone with her son-in-law, which stirred up her sexual desires… She was accidentally seen masturbating by her son-in-law! This was clearly wrong… she shouldn't tell her daughter… and then the son-in-law, unable to resist the allure of the beautiful mature woman, indulged in forbidden lust!