This is the story of the brave men and women who will defend our world. On a desolate road in the snowy mountains, a childless couple wished upon a falling star. The star is revealed to be Galeon, a mechanical lion who delivers the baby Mamoru into their arms. Years later, Mamoru lives the life of an ordinary grade school student, until the day comes when his class is caught up in a ferocious attack by the mechanoid alien Zonders. Just as all hope is lost, the young cyborg hero, Gai Shishio, is sent by the UN alien de fence force 3G, the Gutsy Geoid Guard. He risks his own life without question to protect Mamoru's class and all of Earth. Drawn by the legacy of his mysterious origins, Mamoru becomes a member of 3G, joining the ranks of humanity's bravest defenders. They wage all-out war against the Zonders with their advanced vehicles, weapons and AI robots. When their backs are up against the wall, Gai Fuses with Galeon and 3G's Gao Machines to form the indomitable King of all robots: GaoGaiGar! But even in the face of these awe inspiring machines, the bravery of humanity in its darkest hour is the true Key to Victory!