A boy who came from the heavens encounters a city of ships, Gargantia. In the distant future a young boy, Ledo, is raised in space knowing nothing but war, until he comes to Earth, a planet whose surface is nearly covered in water, where he witness the sea for the first time. On the vast seas with an aquamarine glow, people form huge fleets and live a humble, but happy life. Ledo is the only foreigner in this world with foreign customs and language, but he's not alone. What can he do to make a living here? What should he live for now? His days on this verdurous planet will make him face those questions.