Mariko marries a man whose adult son Yusuke has withdrawn from school. Unable to accept his father’s new wife as his mother, Yusuke keeps his distance even after they begin living together. Hoping to become closer, Mariko promises to support him as family, and he gradually opens up. His problems at school remain, however, and he finally confesses that a failed experience with a woman is the cause. When he asks to learn about a woman’s body, Mariko gently guides her adult stepson, starting with a mature kiss before taking his virginity.