UFO Robot Grendizer vs Great Mazinger

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 humanitys former defender from becoming its destroyer