Pestar was an aquatic monster that had been preying on oil tankers that wandered too close to his territory for a while. He was first spotted by a drunk man, who tried to alert the authorities, but was dismissed for being intoxicated. Once the Science Patrol heard about the monster and noticed the connection to the disappearance of oil tankers, they were called into action to deal with the monster. They first attempted to lure the monster out of hiding with oil barrels from a nearby oil refinery, but it took a long time to lure the monster out of hiding as it was suspicious of the Science Patrol's actions, and fed once the VTOL vehicles were running out of fuel.

Suddenly, a missile was fired by mistake at the monster while it was feeding. Provoked and angry, Pestar headed for the oil refinery and set it ablaze with his flames. Reacting quickly, the monster, due to smoke inhalation, was knocked unconscious. With the flames now out of control at the refinery, the Science Patrol was forced to leave Pestar to deal with the inferno. Luckily, Hayata transformed into Ultraman and managed to put out the fire with ease.