As Japan evolved into a maritime nation, the need arose for specialized schools to teach skills vital to safeguarding the seas. The story takes place at one such all-girls institution. The students enrolled here train to become "Blue Mermaids," combining classroom learning with practical skill instruction. "Blue Mermaids" are women who make the ocean their professional domain. They adhere to the motto "In the sea we live, the sea we protect, and by the sea we go." While they must excel academically, they are also required to cultivate an international perspective. Regarded as the "Elite of the Sea," they are expected to possess knowledge of both their own culture and the customs of other nations.