Dr. Hell and his Mechanical Beasts are back, and they're more dangerous than ever before. Kouji Kabuto and Tetsuya Tsurugi fight a fierce battle against these hellish machines, which are under the command of Baron Ashura. Unfortunately, they are defeated, with Kouji's Mazinger Z being captured and Tetsuya's Great Mazinger seriously damaged by the enemy. The devious Dr. Hell quickly converts the captured robot into Ashura Mazinger and uses it to attack the Photo Power Lab. At the same time, Kouji is missing in action, which leaves Testuya to defend the lab in the damaged Great Mazinger. But the forces of Dr. Hell are too strong, even for a brave pilot such as Tetsuya, and all seems to be lost. The battle seems to be drawing to a close, until an overpowering blast fired by an unknown robot destroys the entire Mechanical Beast army. Could this mysterious robot be the legendary Mazinkaiser, and who is piloting it?

The villainous Dr. Hell has amassed an army of mechanical beasts in his secret hideaway, the island of Bardos located in the Aegean Sea. He is capable of controlling mechanized beasts with his cane, and instructs them to unleash devastating attacks. However, Dr. Hell doesn't do all the dirty work by himself; he has his loyal henchman Baron Ashura to carry out his devilish plans. There are also those that will see to it that evil does not prevail. Kouji Kabuto is the young and feisty teenager with a score to settle: his goal is avenging the murder of his grandfather by Dr. Hell. And he might just be able to pull it off, as he is the pilot of Mazinger Z, a mighty giant robot made out of an indestructible metal known as Super-Alloy Z. Mazinger Z boasts several powerful special attacks. By channeling Photonic Energy through its eyes, and unleashing the Koushiryoku Beam, it can cause great destruction. But things get really cool when Mazinger Z launches its Rocket Punch attack. Dr. Hell and his minions might have just found their match!

Koji is on holiday when the seven generals from Mikene attack the world under the leadership of the general of darkness. How will Kouji be able to stop them? (Source: AniDB, edited)

Kouji and his friends have defeated Dr. Hell and are now enjoying a break, but suddenly a strange prophet appears and warns everyone of an oncoming danger, mechanical beasts never seen before start appearing all around the world wrecking havoc. Its up to Kouji and his Mazinger Z to stand up to this threat but it seems he is vastly outnumber and outmatched. This film served as an alternative link between the Mazinger Z TV series and the Great Mazinger TV series. It basically introduces Great Mazinger to the audience, as well as his enemies from the Mikene Empire.