Shipwrecked, Daisaku (Johnny Sokko) and Juro Minami (an agent for Unicorn) drift to an island and are captured by the BF gang. The island is in fact, a base of the B.F. gang. They happen to discover a huge robot while they are running away.
Emperor Guillotine, king of BF syndicate, plans to take back Giant Robot and to arrest Daisaku (Johhny Sokko), the only one that can give orders to the robot. He sends a huge magic metal globe called Glober to the earth.
Dr. Tadokora develops QQV, a super-excellent transparent metal. He tests it and QQV endures all the attacks of Giant Robot. BF gang watch the experiments using TV cameras and try to rob the specifications of QQV.
Daisaku and Minami happen to help a one-eyes man BF members are chasing. According to the man's story, they are trying to kill him as a traitor because he became frightened by the inhumanity of the syndicate and quit it.
Emperor Guillotine gives Dr. Over a spaceship equipped with all kinds of scientific weapons. After landing at the earth, Over sends an electric monster called Sparky to the ground of a soccer game and kidnaps all 30,000 spectators as hostages.
The underground office of the South Pole Unicorn Branch is buried in red sand which suddenly started to gush out in the ice field. As the communications are cut off, Azuma sends Daisaku and Ninami there to see what happened.
Unicorn members locate the secret headquarters of the Japanese Branch of BF Syndicate. They attack the house and arrest Dr. Over by taking his blue star-shaped metal on his chest, the source of his magical power.
Daisaku and Minami suspect that a strange villa standing in the heart of the Japanese Alps is a secret base of BF Syndicate. They approach the house to get some proof, when men in the house notice them and look for them.
Beginning with the Swiss Branchg, the Unicorn branch headquarters are mysteriously destroyed one after another. Rome, Cairo, Bombay, Singapore, Hong Kong, then Tapai. It is easy to guess that Tokyo will be next.
The Gargoyle Vine is back, and this time it's sucked up all the water in a lake. Will it grow to an incredible size and defeat the combined military might of the Earth? For Dr. Botanus' sake, let's hope so.
The mysterious enemy agent X-7 is assassinating Unicorn operatives around the world with the help of a giant flying hand. As a precaution, Jerry is assigned to protect Johnny, since only U7 can control Giant Robot. That same day, new kid Kenny joins Johnny's class. Coincidence?
The mysterious space man Metron lands in his flying saucer and befriends the Unicorn crew. And yet, it should come as no surprise that he's actually working for Gargoyle. Torozon makes an encore appearance, but Giant Robot literally tears him apart.
The Radion, close relative of the Nucleon, captures Giant Robot and Fangor is going to replace the robot's electronic brain. Johnny and Jerry find the robot. Johnny's tears of frustration reactivate the robot's brain so it can fight Radion.
The Space Mummy has poisoned the water supply so anyone who drinks it is turned into a mummy. Space Mummy and Gargoyle are hiding out in a convent dressed at nuns. Agent U5 is captured and Jerry dresses as a nun to save her. Marie storms the convent with guns blazing to save them. Giant Robot must fight the Starker, a monster that can change size at will. How come Johnny doesn't get to dress up like a nun?
The country of Melcon wants their own giant robot, and Giant Robot's birthday is spoiled by the news. The Melconians build Cleopat, but Goldenaut steals it. Gargoyle scientists can't activate Cleopat, but the robot's reaction defense disables Giant Robot by using his own attacks against him. Even blinded, Giant Robot defeats Tentaclon and throws it at Cleopat, destroying them both.
U7, member of Japan Branch of Unicorn, is the one who controls the gigantic GIANT ROBO with the wrist-watch controller microphone. One day, he receives from his father a parcel as a birthday gift. It is a kit for constructing a man-size robot.
Johnny is shot by a very careless assassin, and Emperor Guillotine pulls out all the stops, throwing his three remaining monsters at Giant Robot. Guillotine then grows to an incredible size and declares himself ruler of the world. Giant Robot can't defeat him, because Guillotine is made of atomic energy and traditional attacks would 'splode the entire world (Chief Azuma's words, not mine). Will Giant Robot make the ultimate sacrifice to save the planet and Johnny?