On a solitary island in the middle of a vast unknown ocean, Dr. Hell, a deranged genius, plans the final stage of his plan for world domination: the activation of his Mecha Beast Army. The only man aware of Dr. Hell’s plan is Dr. Kabuto, a pioneer in new energy sources. In a desperate attempt to stop Dr. Hell before his death, Kabuto uses his research and resources to construct a weapon powerful enough to match that of the Mecha Beast Army, which he entrusts to his grandson, Kouji Kabuto. That weapon is the Super Robot Mazinger Z!