Giant Robo is invincible. Flashes show its past deeds: slaying of Licon, the phantom beast, shattering to pieces the super-robot beast Unbalan, the last sputterig of space plant Santalaws, etc. The Japanese government is asked by the Republic of Merea, the largest power of the world, to reveal the secret of Giant Robo's brain. The fact that Japan has the most powerful robot in the world is embarrassing to the people of Merea, the nation which surpasses every other nation in everything except robot-technology. Japan is on friendly terms with Merea, and the government authorities decide to do as proposed. The news reaches the Japan branch of Unicorn as the middle of the Giant Robo's birthday party and the party is ruined.
