Kaname Okiura, a student at Prefectoral Umineko Shougyou High ("Umishou"), joined the school's swimming club to learn how to swim, but the group is full of weirdos, let alone anybody who can teach him how to swim. The group was then joined by a cheerful, happy-go-lucky female called Amuro Ninagawa, who had transferred from Okinawa. Her exceptional underwater speed and unconventional swimming technique (plus her personal habit of naked swimming—a potent attraction for teenage guys) astounded every club member, notably Okiura, who compares her to a mermaid-like creature he only saw once as a youngster.