The year is 2005, and Tokyo is under siege by extraterrestrial creatures known as Zonders. The Gutsy Geoid Guard, a covert agency, is the only line of defense against these monstrous foes. Their secret weapon? The colossal robot GaoGaiGar, piloted by Guy Shishio, a former astronaut who was nearly killed by the Zonders' first appearance on Earth. A mysterious robot lion, Galeon, saved Guy's life and allowed his father to rebuild him as a cyborg. Now, GaoGaiGar, with Galeon at its core, fights to protect Earth with the assistance of a team of transforming robots and young Mamoru, who possesses the ability to purify the Zonders' cores and a strange connection to Galeon.