Yukika, who had been living alone in the countryside, began cohabiting with her son and his wife in the city. She forgot the loneliness of living by herself and genuinely felt joy in sharing life with her son's family. Six months passed since they started living together, and natural intimacy had formed among the family members. One day, her son suddenly pinned Yukika down and began passionately caressing her body. With age, Yukika's libido had grown stronger, leading her to masturbate daily. Her son secretly watched these moments, and gradually, his own desire began to awaken. Though Yukika resists at first, her son continues without stopping, ultimately ejaculating deep inside her. After that night, Yukika's heart slowly begins to waver. A few days later, she overhears her daughter-in-law complaining about their sexless marriage, causing Yukika to worry if she might be the reason. As Yukika's period ends, a new emotional shift begins to unfold.