Suisei no Gargantia

In a distant future, young lieutenant Ledo and his humanoid weapon Chamber are swept through a distortion of time and space during a battle against the Hidiaazu. Ledo awakens on Earth, a planet at the edge of known territory that he had believed lost. Earth is now almost entirely covered by ocean, and people survive aboard fleets of giant ships by salvaging relics from the depths. Ledo arrives on the fleet Gargantia, where he must adapt to a planet whose history and culture he does not know. He lives alongside Amy, a 15-year-old messenger, and finds himself surprised by the peaceful days that contrast with his life devoted to fighting.