Mamoru was brought to the Earth eight years ago with the lion look-alike robot, Galeon, and grew up as an ordinary boy until aliens began attacking the Earth and Zonderising humans. Guy, a cyborg is a Commanding Officer of the GGG, a secret organization against invasion from aliens. He has the ability to fuse with Galeon to transform into GAIGAR, and through the final fusion, he becomes GAOGAIGAR, a gigantic robot with overwhelmingly powerful strength. Mamoru becomes the only one who can de-Zonderise people.