Nao is married to her husband and lives with her father-in-law. Although sex with her husband is bland, Nao is satisfied, but as months and years pass, the number of days and times they have sex decreases. Nao's sexual desire is so strong that her husband's physical strength is at its limit, and he gives up. Nao has no choice but to masturbate when she is alone to satisfy herself. Her father-in-law observes Nao's life as a married couple and keeps a diary to enjoy. At one point, Nao's clothes changed. Her clothes became more revealing, and she was wearing clothes that could be mistaken for no bra or no underwear. At first, she thought it was part of her sex with her son, but when she looked back at the diary, she realized that she had been dressing like that since the sex with her son had decreased and stopped. One day, her husband went to work and her father-in-law went out on an errand, and while she was enjoying her time masturbating alone, her father-in-law, who had been stood up, returned. Nao's father-in-law stares in shock as she masturbates, but is turned on by her painful moans and takes her under his control. Her father-in-law's experienced caresses are intense, and his persistent cunnilingus makes her cum multiple times. Her father-in-law's penis is bigger, harder and more curved than her husband's, and the moment he penetrates her, she climaxes. A few days later, when her family has gone out and Nao is left alone, she wanders over and takes her father-in-law's underwear out of the laundry basket and gently sniffs it. Remembering her actions with her father-in-law, she runs her fingers down to her crotch, and finds that Nao's underwear is obscenely damp...