A majority of humanity have left the Earth in the far future, and the Galactic Alliance of Humanity is formed to govern exploration and safeguard mankind's prosperity. However, a major threat emerges in the shape of bizarre aliens known as Hideauze, prompting an interplanetary war to save mankind. Ledo, a 16-year-old Galactic Alliance officer, begins the war against the monsters armed with Chamber, an autonomous robot. Unfortunately, during the conflict, Ledo loses control and is hurled out into the vast reaches of space, crash-landing on a wet Earth.