The series is set on a high school, Umisho (short for Kenritsu Umineko Shogyo Koto Gakko ), situated on the island of Itoguchi in Umineko, Kanagawa Prefecture. It begins with an energetic female transfer student from Okinawa, Amuro Ninagawa, joining the school and its swimming team, where she meets the team's manager, Kaname Okiura. Upon meeting Amuro, Kaname feels an attachment to her, as if he had met her previously.
(taken and edited from wikipedia)

Picture	Real Name	Description
	Amuro Ninagawa	Second year student, and a new transfer student from Okinawa at Umisho. Despite her being a dedicated and skilled swimmer, she finds difficulties in performing at competitions due to her not being used to the rules and environment of professional swimming. Among her other uncommon habits, she prefers swimming nude, and has no shame of doing so beside those she got used to, especially Kaname.
	Kaname Okiura	Second year student, and the swimming team's manager. He had a traumatic experience involving a creature he describes as a mermaid during his childhood, and after which he has been afraid of swimming ever since.
	Momoko Orizuka	Third year student, and vice-captain of the swimming team. Just after meeting Amuro, she realizes her hidden potential and recruits her to the swimming team, after challenging her to a match and being impressed with her speed at water.
	Mirei Shizuoka	A second year. Admired by the boys because of her generous measures and polite demeanor, few people know of her repressed lustful desires, and that although she appears to be innocent and pure, she usually wears very mature pieces of underwear.
	Maki Ikuta	A first year student, nicknamed Makio. Too small for her age, she is usually confused with a junior student. Despite being a member of the swimming team, she is still learning how to properly swim by taking lessons from Kaname.