Childhood friends Masaki and Erina plan to go to the beach during spring break, and Tetsu and Shinobu decide to come along. When they arrive at a private beach with a spectacular view, the two couples frolic in the sea and on the shore. Eventually, Tetsu and Shinobu start having sex secretly while napping on the beach. When they look over, Masaki and Erina have seen the whole thing. With no shame or regard for appearances, the two couples reveal their twisted sexual fetishes to each other, and a sex battle begins.