In a post-apocalyptic Japan transformed by colossal tectonic shifts, the nation thrives as a maritime power. Young girls aspire to join the elite Blue Mermaids, guardians of the sea. Childhood friends Akeno and Moeka reunite at Yokosuka Girls' Marine High School, embarking on a journey to fulfill their dream. Assigned to their own ship, the Harekaze, Akeno embraces her role as captain, forging bonds amidst routine training. However, when unexpected challenges cripple their vessel, the crew must navigate perilous waters to prove their mettle as future Blue Mermaids.