After being accepted into university, Tsutomu stayed at his relatives' house, the Kunimi residence, while searching for an apartment. Meeting his aunt again for the first time in years, he found her beauty far surpassing what she had been like in her youth, deeply captivating his heart. One night, as Tsutomu entered the living room, he was shocked to see his aunt indulging in masturbation without attempting to hide herself. Her sight revealed to him, for the first time, the profound allure of a mature woman's body.