Princess Nami, a member of the Azumi royal family, predicted that a terrible monster would appear to wreck havoc on the world. Not long afterwards, archaeologists discovered a shrine dedicated to a guardian monster named King Caesar, along with a sacred statue within the shrine. The cave paintings revealed a prophecy: “when a black mountain appears above the clouds, a huge monster will come forth and try to destroy the world. But when the red moon sets, and the sun rises in the west, two monsters will appear to save the people.”

Meanwhile, a race of extra terrestrials from the third planet of the black hole sent a spy to try to capture the sacred statue of King Caesar. The black hole aliens eagerly desired to halt the reawakening of King Caesar, for if the ancient monster were revived, the aliens’ plan for domination would be in jeopardy as their secret weapon would have to face a monstrous obstacle.

Meanwhile, Godzilla appears at Mt. Fuji, and begins to rampage through the countryside. Anguirus, who was burrowing across Japan, arrives to meet his old friend head on, although not as allies but enemies. The two behemoths clash as the quadruped monster senses that this is not the true Godzilla. Anguirus is hopelessly outmatched, though, as Godzilla ruthlessly cracks spiked quadruped’ lower jaw, which sends Anguirus into retreat. With its foe defeated, Godzilla continued its march toward more metropolitan areas until it was met by another adversary: a second Godzilla! Allowing for the revelation that the first monster wasn't Godzilla at all, but instead a mechanical clone of the King of the Monsters named Mechagodzilla. The mechanical menace quickly sheds its disguise, once the tides of the battle turn against it, and goes at Godzilla with full force. Its overwhelming power sends Godzilla into retreat, but the attack takes its toll on the robot as well, forcing the black hole aliens to recall their war machine in order to repair it.

The black hole aliens didn't stay idle in their bid for world domination, though, as they continued to try and seize the sacred statue, which was on route to be returned to the Azumi Castle gate in order to fulfill prophecy. However, the alien's opposition failed, and the statue was finally returned, just as the red moon had set and the sun was rising, while reflecting off the clouds to give the illusion that it was rising in the west as the prophecy had foretold. The energy from the sun glowed in the eyes of the artifact, and a focused beam of brilliant energy struck a rock formation in the nearby sea. Princess Nami's sang an ancient song, and a monster emerged from the formation. King Caesar, after centuries of rest, was finally revived, and it would soon clash with Godzilla’s bionic doppelganger!

With repairs finalized, Mechagodzilla was dispatched to destroy King Caesar. The mammal-like monstrosity entered the fray and began his assault by reflecting the cosmic monster’s eye beams with his own eyes. Fierce finger missiles soon gave the cold machine the upper hand, and it started to severely outmatch King Caesar. Fortunately, Godzilla arrived on the scene just in time, craving vengeance for his past humiliation at the hands of his mechanical clone. With the two monsters fighting off Mechagodzila, the prophecy was finally coming to fruition. However, the Mechanical menace proved to be too much for both King Caesar and Godzilla. Godzilla was brutally injured, and had to quickly find a method by which to defeat his adversary. He suddenly converted himself into a giant organic magnet, causing every metallic object in the surrounding area to be attracted to him. Mechagodzilla could not escape from Godzilla's magnetic grip, and King Caesar proceeded to head butt the mechanical dragon in the right side of its chest. With Mechagodzilla having sustained heavy damage, Godzilla finishes off the sadistic, cybernetic clone, by twisting the head of the menace off. Mechagodzilla was completely annihilated in the process, exploding on the coastal cliff as fragments of space titanium were sent off into the waves below. The aliens’ plans for domination were finally thwarted!

King Caesar returned to the rock formation from whence it came, and the royal Azumi family regained possession of the statue. The royal family would continue to protect this sacred statue of their guardian monster long into the future.