Masaki and Erina are childhood friends. The two of them made plans to go to the beach during spring break, and Tetsu and Shinobu decided to go with them. When they arrived at the stunning private beach, the two couples frolicked in the sea and on the shore. Before long, Tetsu and Shinobu secretly started having sex while taking a nap on the beach. When they glanced next door, they saw that Masaki and Erina had witnessed everything. Without shame or regard for appearances, the two couples began to flaunt their twisted sexual fetishes, and a sex battle began.