A young boy aids in the fight against a terrorist organization as the sole controller of a prototype giant robot.

Johnny Sokko is an ordinary boy whose life takes an extraordinary turn on a boat voyage when he meets Jerry Mano, a young man who befriends him. The boat is suddenly sunk by the minions of the terrorist organization known as the Gargoyle Gang, who have a habit of using giant monsters and giant robots in their attacks. Finding themselves on a Gargoyle island base, the pair meet up with a scientist who has constructed the most advanced and powerful giant robot of all. Concerned that his creation will be used for evil purposes, the scientist shows the pair the robot and its wristwatch voice controller which is programmed to imprint on the first person who speaks into it and make that person into the only person who can control the robot from that point on. Impulsively, Johnny speaks into it himself and thus becomes that person. With the robot's help, they escape from the island and Johnny learns that his new friend Jerry is an agent of the worldwide intelligence and anti-terrorist organization known as Unicorn, which is dedicated to fighting the Gargoyle Gang. With no other alternative open to them, Unicorn quickly recruits Johnny as a full and regular agent. Now, Johnny has a vital role in this new war as the one person who can bring the tremendous strength and weapons of Giant Robot (the name that he gives the robot) to bear against the forces of evil.—Anonymous