After Natsumi discovers an adult DVD under the futon while putting it away following her son Hiroshi's departure for school, she questions him about it. Normally gentle, Hiroshi erupts in furious anger, leaving Natsumi confused and unsettled. That night, as she lies on the sofa, she wakes to catch Hiroshi peeking under her skirt. When she confronts him about his recent behavior, he confesses his growing curiosity about women's genitals. With no husband to rely on, Natsumi had resolved to raise her son strictly on her own—but as she begins responding to his demands, their relationship spirals into increasingly intimate territory.