The story take place just after the end of Getter Robo when the empire of the Oni, some sort of demons in the japanese mythology, wipes out the enemies of the first series: the dinosaurs. The primary goals of the oni's empire, whose leader is the emperor Brai, it's to take over the world and the getter rays technology. Dr. Saotome builds a new Getter Robo, the Getter Robo G, that is much stronger than the first one and still composed by three getter-machines: Dragon, the red one, Ryger, the blue one (instead of the white one of the first series) and Poseidon, the yellow one. The Getter's pilots are the same except for the third getter-machine where Benkei has replaced Musashi.