Alien invaders take over Great Mazinger who is at the entrance of a museum next to Mazinger Z as symbols of peace. Grendizer fights the evil invaders and Great Mazinger is recovered. When the Vegan empire dispatches a new general to oversee the takeover of Earth, he quickly manages to capture Koji Kabuto and, learning of Great Mazinger through interrogation, quickly commandeers it from a museum where it was kept as a symbol of peace. It is now up to Duke Fleed aboard Grendizer to stop humanity's former defender from becoming its destroyer.
| Directing | Osamu Kasai | Director |
| Writing | Keisuke Fujikawa | Screenplay |
| Directing | Johei Matsuura | Assistant Director |
| Writing | Go Nagai | Original Series Creator |
| Production | Chiaki Imada | Producer |
| Visual Effects | Yuki Kinoshita | Key Animation |
| Editing | Chikako Matsubara | Editor |
