Spring 1976

Five youths exploring a rocky island near Edo City discover the machines created by scientist Doctor Hoarai for a war no one believed was coming. Hoarai had warned that a subterranean race of rock people would invade the surface, only to be mocked by his peers. By the time his prediction comes true, his body is gone, but his mind remains inside a computer to guide those willing to fight.Led by Youko Misaki, the youngsters take control of Hoarai's vehicles and the giant robot Gordam, becoming the Gowapper 5. Still inexperienced and often reckless, they must learn to operate as a team while the subterranean army launches its assault on humanity.

A newly appointed Vegan general captures Koji Kabuto and learns through interrogation that Great Mazinger is preserved in a museum as a symbol of peace. The invaders steal the dormant machine and turn one of humanity's greatest defenders into a weapon aimed at Earth.Duke Fleed launches Grendizer against the hijacked Great Mazinger, but destroying it would mean losing an irreplaceable ally. He must withstand its overwhelming attacks long enough to free Koji, recover the machine, and stop the Vegan force behind the assault.