One night just before summer vacation, Daichi Manatsu, a second-year high school student, spots a strange circular rainbow hovering in the sky above Tanegashima and heads there alone. He has seen this rainbow before. Carrying memories of his father's mysterious death and an encounter with a mysterious boy and girl, Daiji arrives on the island as the alarm of a building labeled "Earth Engine" sounds. Someone asks him if he is a captain, just as robotic intruders from Uranus called "Kiltgang" arrive. The battle around the shining stars is about to begin.