Azumi Abe is captain of the Shinano, a Yamato-class battleship from Maizuru Girls' Marine High School with the designation M-119. She commands her ship and crew alongside her executive officer, Tsubame Kawano, leading a delegation to an annual interschool competition in Yokosuka. The Shinano is marked by distinctive yellow stripes. When pirates seize a water purification plant and deploy a mobile seafort, the competition is interrupted. Azumi and the Shinano join a combined task force composed of student crews from various marine high schools and vessels from the Blue Mermaids. Their mission is to retake the purification plant and neutralize the threat of the heavily armed seafort. Her given name, Azumi, combines the characters for "second, Asia" (亜) and "clear, pure" (澄). Her surname, Abe, is written with the characters for "Africa, flatter, fawn upon, corner, nook, recess" (阿) and "part, department, category" (部). This surname is also borne by Imperial Japanese Navy Rear Admiral Abe Toshio, who commanded the aircraft carrier Shinano during World War II.