Sango Shou Densetsu: Aoi Umi no Elfie

Synopsis

In a future where human disregard for the environment has caused sea levels to rise and submerge every continent, only scattered islands remain. Elfie lives on one such island-city with her grandfather. After an accident underwater, she discovers she can breathe in the ocean. Her grandfather then reveals that she is actually one of the mythical sea-folk. Local politicians exploit the islanders' fear of outsiders to instigate a war against these hidden people, using it as a distraction from their own resource shortages, and Elfie finds herself caught in the middle of the conflict.