Haifuri (High School Fleet) - A hundred years after catastrophic shifts in tectonic plates caused most of its area to submerge, Japan now thrives as a maritime nation. High functioning cities line the coasts of Japan, and well developed sea routes are defended by specialized naval ships. The marine industry is flourishing, and young girls are eager to join the Blue Mermaids—highly skilled women who devote their lives to protecting the seas. After some time apart, childhood friends Akeno Misaki and Moeka China are reunited at Yokosuka Girls' Marine High School. Here they are joined by others who share their dream of becoming Blue Mermaids. Soon, training exercises commence, with Akeno and Moeka being put in charge of their own ships and crew. Everything is progressing smoothly for Akeno as she settles into her role as captain and builds camaraderie between her fellow crew members aboard the Harekaze, a destroyer ship. However, unexpected engine and navigation failures soon leave their ship stranded and the crew in danger. High School Fleet follows the Harakaze's valiant crew as they navigate treacherous waters and other obstacles on their quest to become fully fledged Blue Mermaids. ハイスクール・フリート(はいふり) - 海に生き、海を守りて、海を往く―― それがブルーマーメイド! 今からおよそ100年前、プレートのずれにより、多くの国土を水没によって失った日本。 国土保全のため、次々と築かれた水上都市はいつしか海上都市となり、それらを結ぶ航路の増大に伴い、 海の安全を守る多くの人員が必要となっていった。 それに伴い、女性職業の会場進出化も進み、海の安全を守る職業「ブルーマーメイド」が女生徒たちの憧れとなっていった。 そんな時代、幼馴染の岬明乃と知名もえかは、「ブルーマーメイド」になるという同じ目標を持つ仲間たちとともに、横須賀の海洋高校に入学する。
