A race of humanoid aliens with faces that resembled apes, the extraterrestrial beings traveled through the stars to search for a new home as a Black Hole was destroying their old habitat. Eventually they found it on the planet Earth and began to infiltrate it while disguising their faces as humans. However, if one were to die the disguise would fade away and reveal their true form. Learning about Godzilla, they studied the King of the monsters for some time before using this information to create their ultimate weapon to defeat him: a large robot known as Mechagodzilla.

It would not be long before agents of Interpol, the famous international law and police cooperation organization, found out about the alien race and began to track their activities. Operating from a base in Gyokusen Cave in Okinawa, the Black Hole Aliens at first were greeted with success as their war machine, in the guise of Godzilla, claimed its first victory against the monster Anguirus. Later, the towering robot also successfully defeated Godzilla, although the damage the giant machine suffered necessitated repairs and a delay in the attack on Tokyo. At the same time, the aliens were tracking down several human scientists and archeologists who had stumbled upon a statue in Okinawa that had the power to unleash a fierce deity known as King Caesar.  Despite their best efforts, the scientists managed to awaken King Caesar, who soon became the first target of the repaired Mechagodzilla. The war machine soon had King Caesar on the run until a revived Godzilla showed up to once again face his mechanical double. Despite heavy fighting, the two kaiju managed to destroy the alien machine while the combined efforts of the scientists and Interpol agents destroyed the Okinawa base of the Black Hole Aliens along with all the extraterrestrial occupants inside.

Undaunted, the aliens continued with their attempts to conquer Earth. Under the command of a Black Hole Alien named Mugal and operating at first from a base in Mount Amagi, they recovered the remains of the destroyed Mechagodzilla while securing the assistance of disgraced Japanese scientist named Shinzo Mafune. In doing so, they also acquired use of the monster that he controlled, a dinosaur by the name of Titanosaurus. After saving the life of Mafune’s daughter a second time and installing a control device for Mechagodzilla inside her, the Black Hole Aliens launched their offensive with a devastating attack on Tokyo as they demonstrated the combined might of the improved Mechagodzilla and Titanosaurus. Fortunately, like last time, the efforts of Interpol and Godzilla stopped the aliens attempt at world conquest. For good measure, Godzilla blasted the last of the Black Hole Aliens as they attempted to retreat to the stars from which they came in their spaceships.