Eternal Arcadia: Kuuzoku Weiss Sanjou!

Thousands of years before the events of Skies of Arcadia, six civilizations coexisted on floating continents in the titular skies of Arcadia, a world with no apparent surface that is orbited by six moons of different colors. The civilizations, one of which existed for each moon, developed technologically to the point where each created a Gigas, a colossal living weapon of mass destruction, as well as the Moon Crystals that could be used to control them. Using the Gigas, the civilizations warred with one another, which caused enormous environmental harm and threatened the extinction of all six civilizations. The most advanced of the civilizations, the Silver Civilization, used their Gigas to summon the Rains of Destructio...