The main character is Yu Arahama, who has five sex friends, Misako Shimizu, a colleague at the company, Ryoko Yanagi, who runs a coffee shop near Arahama's apartment, Kotori Hoshino, a female student he knows, and Kotori Hoshino, the female president of a large company. The five heroines, including ``Kamishima Aina'' Arahama and Misako, who met on a dating site called ``Makiko Endo'', came to the beach at the suggestion of Arahama, who was tired of having sex at her home. ``It's the ocean!'' the heroines exclaim, throwing off their clothes and diving into the ocean, each with their own watermarks already written underneath. The five heroines splash water on each other in the sea and bounce around with beach balls.