Mio, a member of the swimming club, is dating Takumi, a boy from the cultural club at the same school. Just sitting next to him makes her heart pound so hard she thinks it will burst. Holding hands, kissing... everything about their love is like a page from the innocent youth of their youth. Mio was living such a happy life until one day, during club activities, the swimming club advisor, Mr. Oki, sexually harassed her by fondling her breasts, groping her pussy, and grabbing his penis, and in the end, he even forced it into her pussy. However, she becomes addicted to sex with the married teacher's skilled penis - and they end up having an affair every week at the pool after school.