Kenko Zenrakei Suieibu Umisho

Kaname Okiura, un estudiante de la prefectura Umineko Shōgyō High School. Escuela Secundaria del Distrito Comercial Umineko ("Umisho" para abreviar), se unió al club de natación de su escuela, con el fin de aprender a nadar. Pero el club está formado por 5 chicos (incluyéndolo) y 12 bellas chicas (o al menos eso parece), que para nada le enseñaran a nadar, así que se hace entrenador del equipo. En un día bastante soleado dos personas en un bote (con una casa encima) llegan a la costa. Una de ellas es una chica muy alegre llamada Amuro Ninagawa, una estudiante transferida desde Okinawa, y la otra persona es su padre. Ella de inmediato se une al club de natación, su extraordinaria velocidad y el estilo de natación un poco ortodoxo (y su personal hábito de nadar desnuda - un poderoso imán para los chicos) sorprendió a todos los miembros del club, especialmente Okiura, porque ella le recuerda a una sirena que vio sólo una vez en su infancia.

Within the Kanagawa prefecture lies the seaside city of Umineko. There, Kaname Okiura, a student in his 2nd year of high school, attends Umineko Shōgyō High School. Seacats Commerce High School, or Umisho for short. He is also the manager of the Umisho's swim team though he himself doesn't know how to swim. In fact, he is afraid of the water stemming from an incident which occurred some years ago. While he was at the beach, he had nearly drowned when a 'mermaid' pulled him under the water. He joined the school's swimming club in order to learn how to swim, but the club is filled with weirdos, who don't teach him swimming. One day, a floating house arrives at the shores of Umisho bearing two persons. One of these is a cheerful, sunny, happy-go-lucky girl named Amuro Ninagawa, a transfer student to Umisho, and the other is her father. Her incredible swimming speed makes her an instant hit with the swimming club, but Okiura is surprised, as she reminds him of the mermaid he saw only once in his early childhood. After her floating house is destroyed during a storm she moves to Kaname's house.