Many millennia ago, an ancient civilization genetically engineered a race of birdlike demons called the Gyaos. Though they were created to rid the world of pollution, these horrible harpies began to prey on the people, and slowly this advanced civilization was wiped off the face of the planet. With their prey dwindling, the Gyaos fell into a deep hibernation until the time was ripe for their reemergence.

A Gyaos nest lay dormant for many thousands of years, until the conditions were just right, and the eggs hatched. Calling out for food, the loathsome creatures were met with no response. The disgusting monstrosities were left with one repulsive alternative: cannibalism. A trio of terrors survived the gruesome feast, and the grotesque goblins began preparations to sharpen their abilities and learn how to fly. As their range began to increase, the human inhabitants of the island started to meet a hellish fate. In time, not one person was left alive in the vicinity.

As the vile, voracious Gyaos continued to increase their hunting grounds to new islands, the military began to formulate a plan for their capture. The Gyaos would be led into a baseball stadium, and the roof would be closed. Troops would then tranquilize the trapped terrors, and the mission would be a success. In words, it was brilliant; however, the actual execution was a disaster. The Gyaos were lured into the stadium through the use of meat, but the crimson creatures grew suspicious. One sergeant panicked and ordered his troops to fire at the Gyaos prematurely. Two were brought down, but one escaped!

As helicopters pursued the fleeing Gyaos, a titanic turtle suddenly appeared. The guardian Gamera, recently awoken from a long slumber, quickly slew the contemptible creature. Sensing Gamera's arrival, the remaining Gyaos used their sonic beams to escape from the stadium. Gamera pursued the foul fiends to a mountain village, where the heroic turtle slew yet another of the deplorable demons. The military did not recognize that Gamera was a benign beast, and an attack was launched on the massive monster. With the synergistic assault of both the military forces and the remaining Gyaos, Gamera had to bid a hasty retreat. Unopposed, Gyaos was allowed to feed and grow into an even greater form: Super Gyaos.

One Gyaos managed to survive its battle with Gamera, and the contemptible creature continued to feed off animals and humans alike in the Japanese countryside. It grew increasingly larger, until it finally became the massive Super Gyaos! With its new incredible size and strength, Super Gyaos targeted what he perceived as a massive buffet: Tokyo. It entered the city, and ripped a train from its tracks. In a repulsive display, it ingested the contents of the vehicle in a nearby park, where it rested for the night.

The next day, the military shifted its focus from Gamera to the new crisis: Gyaos. A military strike on the demon bird failed in the park, and the vicious monster fled into the city. Two missiles were launched at the beast, but the creature swung around Tokyo Tower, confusing the targeting systems and resulting in the annihilation of the famous landmark. Gyaos circled the area and landed on the decimated tower, where it rested for the night.

Though this one creature had brought the massive metropolis to its knees, the military wasn't deterred. Another plan of attack was organized for execution, but the quaking Earth signaled the arrival of an entity that would make the upcoming strike unnecessary. Gamera had burrowed his way from the sea, where he had been resting and healing from his earlier battle with Gyaos and the military. Now, he was ready to fight once more! He unleashed a plasma fireball on Gyaos, but the flying terror fled. Its nest wasn't so lucky; for the flaming sphere erupted the nest into a raining shower of shattered Gyaos eggs. Gamera took to the air once again and pursued Gyaos across the urban sprawl, until his enemy's sonic beam knocked him out of the sky. Gamera crashed into civilization, and Gyaos quickly swooped down to tear the guardian apart. Though both of the ancient beasts battled furiously, Gyaos lost the upper hand when Gamera sliced through its leg with his elbow blade, knocking the man-eating devil bird backward into a building. Gamera lifted into the sky, and his infuriated foe followed. The two raced straight up and out into the furthest reaches of the atmosphere, until Gamera's propelling rockets failed him. Gyaos caught up with the stalled turtle, and both creatures became locked in mortal combat as gravity pulled them back toward the Earth. Even the extreme heat and pressure of reentry didn't seem to faze the monsters. Finally, Gamera bit Gyaos' injured leg off and shoved himself away from his adversary. The plummeting turtle fell into an oil refinery, causing a massive explosion that completely engulfed him. Super Gyaos fired at the remaining buildings in the vicinity, causing them to erupt in a raging conflagration as well. Something mysterious began to occur, however. The fire began to twist and converge into the center of the explosion. Absorbing all of the flames, Gamera flashed brightly and roared as he fired a single massive fireball, which decapitated and destroyed his dumbfounded foe. The sadistic, sinister Gyaos' reign of terror was finally over.

The Gyaos were not extinct, however. This battle would only prove to be among the first in a long and horrible war against these detestable demons, who would eventually evolve into a larger and much more terrifying form: the Hyper Gyaos...

The technique that Gamera had utilized to save the Earth from the swarm of ravenous Legion quickly placed the planet itself in dire jeopardy. The Earth's natural levels of mana, already decreased by pollution, were severely depleted by Gamera's use of the energy weapon. Due to the lack of mana, clutches of Gyaos eggs began to hatch across the world. These deplorable demons had been waiting for such conditions to rise again, and with such a vast breeding population, the contemptible creatures evolved into a larger and far more unspeakable evil: the Hyper Gyaos!

Sensing the return of his arch nemesis, Gamera rose from the sea to battle against his frightful foes once more. Reports of the ongoing monster war were coming from every corner of the planet, and finally, two Hyper Gyaos arrived in Tokyo! Gamera followed in quick pursuit, and shot one of them out of the sky over the Shibuya District. The burning abomination began to plummet into a train station, turning the once peaceful Tokyo night into a chaotic nightmare! Gamera landed, ever searching for his enemy. He located an injured Gyaos with a broken jaw; it was unable to fly. Refusing to show any mercy for these twisted beings, he wiped the winged terror off the face of the planet with a single fireball. The resulting explosion engulfed an entire city block, and Gamera bellowed into the night. He continued his search for the remaining Gyaos, carelessly laying waste to everything in his path. Another Gyaos appeared and attacked Gamera with its beam of sonic distortion. Gamera paused to spare a child from the wrath of the beam, before firing at his attacker in retribution. The grotesque goblin evaded Gamera's fireballs, causing them to crash elsewhere in the urban sprawl, killing thousands of helpless people. Finally, Gamera launched three balls of intense power, which finally destroyed the demented demon. Its remains rained on the city below, causing the unfortunate demise of many more people. Gamera rocketed into the sky to continue his personal war against the monstrosities he was built to annihilate, as a great portion of Japan's capital lay in ruin.

In Kyoto, the guardian terrapin was soon occupied with a massive, mutated Gyaos named Iris. As a result, the Hyper Gyaos were able to group in massive numbers all across the globe. Enormous hordes of the creatures began converging on Japan, in an effort to rid the planet of Gamera once and for all. Upon Iris' defeat, the nations of the world finally joined the heroic turtle in his quest to save the earth from the invading Gyaos. The war machines of humankind joined Gamera, as they prepared to face the great shadow of evil head on!