Soon after the events of the Dinosaur Empire invasion, Earth finds itself under attack by the Pandemonium Empire and its fleet of giant battle robots. In response to the threat, the Copernicus Laboratory re-fits its chief weapon: three advanced jets, capable of merging into three distinct robots. These are Star Dragon, the most powerful and oft-used formation; Star Arrow, designed for speed and aerial combat; and Star Poseidon, built for strength and aquatic battle.