Humans have left Earth and have made a paradise in space, Avalon, as humanity's new home and created the Galactic Alliance of Humanity to expand their journey through it. A threat known as Hideauze appeared before the Alliance and a war rages between them. Ensign Ledo and his artificial intelligence robot partner, Chamber, join the latest attack against the Hideauze. The attack eventually ends in failure and a retreat order is issued, but Ledo is unable to return and is cast out into space. Six months later, the salvage ship Gargantia retrieves Chamber from bottom of the ocean, but are unable to take it apart. After everyone leaves, Ledo decides to take a look around and gather intel on where he is, but Ledo is soon chased and kidnaps one of the crew, Amy. He is chased outside and finds out he is on a habitable planet, which shocks him enough to release Amy. The crew pins him on a pylon, and he calls Chamber, which the entire crew is surprised to see moving and floating.