The story sets in Japan's near future. Dr. Nobuhiko Komyoji who was the authority on robot engineering originally took charge of "ARK Project," Japanese government's national project to use robots peacefully to solve the problems beyond human control. One year after the sudden death of Komyoji
during an experiment, the project has been taken over by Komyoji's rival Kanzaki and the Minister of
Defense Tsubakiya, and has started losing its original object. Then Jiro/Kikaider, an android with a conscience
circuit created by Komyoji, gives battle to the project and tries to protect Komyoji's daughter and son, Mitsuko
and Masaru, who have the key to complete the project.