Tsubumi is a member of the swimming club and practices every day. Natsume is a beautiful teacher who works as an advisor to the swimming club, targeting the buds. Natsume uses her position as a teacher to instigate Tsubumi in lesbian sexual harassment. Serious Natsubud accepts it because he thinks it's for swimming. Tsubumi, who was a straight guy, unwittingly reacts to Natsume's naughty tongue technique, and learns of lesbian orgasm. Will she continue to fall into soft lesbian sex, which is different from that of a man?