While fighting with some of his enemies Mazinger Z inadvertently knocks them into a volcano, where they crash into the prison of the Satan race and release Pheonix Jenny! Dr. Hell, learning of this, frees the rest of the Satan race and teams up with them to defeat Mazinger Z, and their ability to fly proves to be too much for our hero. Meanwhile, Devilman is also individually fighting the members of the Satan race, but their combined power is too much for him as well; can Mazinger and Devilman put aside their differences and team up to defeat Dr. Hell and the Satan race?

Dr. Hell, Mazinger Z's main enemy, has been defeated and killed in battle, and finally Kouji Kabuto and the rest of his friends can take a break from their duty of defending Japan and the world from evil. However, during a storm after a very hot day in the beach, Boss, Mucha and Nuke have a disturbing vision of a prophet that heralds the end of the world, claiming that the dead will raise and destroy the human race, and that the General of Darkness will attack from air, sea and land. The only hope of defense is an iron fortress, Mazinger. After these words, the strange figure disappears. When Boss tells these events to Koji and Sayaka, they barely credit what he says, mocking him and disregarding this prophecy as only an illusion caused by the intense heat. They start listening to music on the radio, but are soon interrupted by reports of attacks by bizarre monsters in several important cities including London (attacked by Aquatic Beast Arimoth), Moscow (by Reptile Beast Gurosten), Paris (by Superhuman Beast Arsoth), and New York (by Aerial Beast Orbee). In his base, Archduke Gorgon, who had outlived Hell and his servants, rejoices while watching the attacks, and decides that now it's Japan's turn to fall. At his command, beasts Dante, Saraga, Birdian, Raigon, Mommothos and Suruba emerge from the sea, heading for Tokyo. These are later revealed to be the Mikene Empire's Warrior Beasts. In the Photonic Research Institute, Koji takes control of Mazinger and flies to the city, while Diana A and Boss Borot watch the monsters fly in direction to Tokyo. When he finally finds the monsters, Koji is surprised by the fact that unlike anything he had ever faced before, they are able to speak and seem to have a mind of their own. Mazinger had previously fought against Gorgon's monsters, but these are some of Mikene's finest, and won't be so easy to take down. He is first lured into the sea where he has to deal with the fierce Suruba, but manages to d...

Once again, Dr. Hell has pitted himself against Mazinger Z - but this time, he actually succeeds! Armed with an electromagnetic ray and net, Dr. Hell manages to capture his arch nemesis and put him out of commission; and with Mazinger Z no longer a threat, Dr. Hell then attacks the Photoatomic Research Institute as the last obstacle in his quest for world domination. Boss and Aphrodite are doing their best to defend it, but can they really defeat the man who beat Mazinger Z? Will Dr. Hell finally achieve world domination, or will our hero find a way to break free and fight once more?