With Japan having developed as a maritime nation, it became necessary to have specialized schools to teach skills essential to protecting the sea. The setting is one such all-girls school. The girls who enroll here study to become "Blue Mermaids," through classroom instruction and teaching of practical skills.
"Blue Mermaids" are women who pursue the ocean for their professional occupation. They live by the motto "In the sea we live, the sea we protect, and by the sea we go." They must excel in their studies, but must also adopt an international mindset. They are the "Elite of the Sea," and are expected to be knowledgeable of the customs and cultures of other countries as well as their own.

(Source: Anime News Network)