ダイソン球
The story takes place in an unspecified future date, referred to as the 71st year of the . Seventy percent of all human beings have migrated from Earth to other planets of the Solar System and a Dyson sphere, constructed around an artificial Sun. The world is divided between two superpowers called the and the (ARUS), and a neutral nation called , the Japan and Islands of Oceanian Republic, that has prospered economically. In the same year, the Dyson sphere, built by JIOR, is invaded by the Dorssian military forces.