A man fell into the desert and lost his memory. He was adopted by Koji Kabuto and named Daisuke. With the wealth created by the fantastic clean energy photon force, Koji Kabuto became a tycoon and a partner of justice. The two-faced man placed his trust in Daisuke, an extraordinary and talented person. When the peaceful days seemed to continue, unidentified aerial phenomena appeared above major cities around the world. It was an invasion by the Vega joint forces from a distant galaxy. Humans were ravaged by Vega, and their weapons were far inferior to Vega's weapons. The steel city Mazinger Z stood up from the blue water, and the last hope of the earth was in trouble in front of the alien weapon Diskmon. In desperation, the demon god Gurentaisha from an alien planet appeared, stirring up dust. Driving it was Daisuke, who was Duke Freed, a prince who was expelled from his hometown Freed──