Mamoru was an ordinary grade school student until the day his class trip gets caught up in a ferocious attack by the mechanoid alien Zonders. The young cyborg hero, Gai Shishio, is sent by the UN alien defence force “GGG.” He risks his own life without question to protect Mamoru’s class and all of Earth. Drawn by a mysterious power, Mamoru becomes a member of GGG, 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 GGG’s Gao Machines to form the indomitable King of all robots: Gaogaigar! In the face of these awe-inspiring machines, the bravery of mankind in its darkest hour is the true Key to Victory!