Tsubomi, a member of the swim team, is dedicated to her daily training. Targeting her is Natsume, the beautiful and seductive coach of the swim club. Abusing her position as a teacher, Natsume begins sexually harassing Tsubomi with lesbian advances. Believing it's for the sake of her swimming, earnest Tsubomi reluctantly accepts. Though previously straight, Tsubomi involuntarily responds to Natsume's lewd tongue techniques, experiencing her first lesbian orgasm. Gradually, she becomes drawn into soft, intimate lesbian sex—something entirely different from being with a man.