Eternal Arcadia: Kuuzoku Weiss Sanjou!

Before the events of Skies of Arcadia, six civilizations lived on floating landmasses in a sky-world with no visible ground and six colored moons. Each civilization built a Gigas, a massive destructive weapon, and developed Moon Crystals to control them. Conflict between the civilizations led to environmental devastation and near extinction. The most advanced, the Silver Civilization, used their Gigas to trigger the Rains of Destruction, which rained meteors from the moons and halted the war. The Silver Gigas was sealed, and the Moon Crystals hidden. In the present, the Valuan Empire, ruled by Empress Teodora, seeks the Crystals to awaken the Gigas and conquer the world. The Valuan Armada, commanded by Galcian and Ramirez, enforces the Empire's rule. The Blue Rogues, a group of air pirates, oppose them. Fina, a girl from the Silver Civilization, searches for the Crystals to protect them from Valua.