One night right before summer vacation, Daichi Manatsu, a second-year in high school, sees a weird round rainbow floating in the sky above Tanegashima and ventures there alone. He has seen this rainbow before. With the memories of his father's mysterious death and an encounter of a mysterious boy and girl, Daiji arrives on the island while the alarm of a building labelled "Earth Engine" is going off. Someone asks him if he's a captain, just as robotic intruders from Uranus called "Kiltgang" arrive. The battle around the shining stars is about to begin.