母親と2人暮らしのタカシ。ある日タカシの幼馴染の七緒がやってくる。母親は息子の成績の悪さを心配し七緒にタカシの家庭教師を頼む。地味陰キャだが委員長肌で責任感の強い七緒はそれを引き受けタカシに勉強を教えることに。勉強熱心な七緒はタカシと勉強をしていくが、ある時タカシの部屋でエロ本を見つけてしまう。エッチな事に興味津々な七緒はオナニーが見たいと言い出し…。

Takashi lives alone with his mother. One day, his hood friend, Nanao, comes to visit. Worried about her son's poor grades, his mother asks Nanao to tutor him. Nanao, a quiet and introverted girl but with a strong sense of responsibility and a class president-like personality, accepts the job and begins teaching Takashi. Nanao is diligent in her studies, but one day she finds an erotic magazine in Takashi's room. Intrigued by all things sexual, Nanao asks to see him masturbate…