Set after the final defeat of the Dinosaur Empire and the death of Musashi Tomoe in the original Getter Robo series, Getter Robo G follows Dr. Saotome, the creator of Getter Robo, as he worries that the peace his team has secured will be brief and that a more powerful enemy may emerge. His concerns are confirmed when the militaristic Hyakki Empire, also known as the Hundred Demons, arises. Prepared for this threat, Dr. Saotome develops an even more powerful Getter Robo, Getter Robo G, and establishes a new Getter Robo base. With Musashi gone, he needs a third pilot and recruits baseball player Benkei Kuruma to fill that role.