Professor Gill leads the secret, evil organization Dark, which is building savage androids in a scheme for world domination. Doctor Komyoji and his daughter Mitsuko have been taken prisoner by Dark and are forced to develop androids for them. In defiance of Dark’s ambitions, Doctor Komyoji secretly builds a robot for justice, the android Jiro. To fight against the androids of Dark, who might even be called his brothers, the artificial humanoid Jiro can transform into Kikaider. Though his “conscience circuit” is incomplete, he resists the controlling sound waves of Gill’s flute, and fights a harsh battle for justice.