In Gamera vs. Gyaos, Gyaos appeared in Japan from a large cavern, and feasted on blood, principally that of livestock and humans. Soon, Gamera confronted Gyaos, and after a battle, Gyaos was forced to flee, and Gamera was forced into the ocean to recover. It is soon learned that light causes Gyaos' skin to shrink, so the light of the city stadium of Nagoya kept Gyaos at bay. Gamera soon returned to finish Gyaos off and, after a battle in the air, Gyaos cut off his own foot to escape from the sun.
The protagonists developed a plan to place artificial blood on a rooftop in Nagoya. The plan was to keep Gyaos drinking the blood for so long that the sun would come up and kill him, while a rotating platform would make him too dizzy to fly away and eventually burn in the sun. But Gyaos proved more cunning than originally thought and expelled a yellow fog attack from two nozzles in his armpits to protect himself from the sun (as well as put out the fires in the engine room). The next plan was to lure Gamera to Gyaos' lair in the forest by setting the forest alight. Gyaos used his fog attack to put out the flames, but Gamera arrived and eventually defeated Gyaos, wounding him many times and biting his throat, leaving him unable to escape the sunrise. Weakened by the light, Gyaos collapsed and Gamera finished him off by throwing the beast into Mount Fuji.
