Mio lives with her parents and younger brother. One day, after her brother finds a porn magazine on the street and discovers the act known as "konnyaku masturbation," she decides to teach him proper sexual knowledge by using her own body. This film portrays the gentle, earnest, yet sexually curious older sister carefully guiding her younger brother through sex education. Set within a warm, affectionate sibling relationship, the story unfolds in an approachable, intimate atmosphere.