Ledo, a soldier of the space-faring Galactic Alliance, is thrown through a wormhole mid-battle and crash-lands with his mecha partner Chamber on an ocean-covered Earth, reshaped by rising seas into an archipelago of scavenger fleets. Taken in by the fleet ship Gargantia, he learns from messenger Amy and commander Ridget to live without orders or a war to fight, while Chamber quietly studies the culture that surrounds them both.