A man made monster, Jirass lived in the bottom of a lake after his creation by an insane scientist with a dinosaur obsession. His presence in the lake caused fish populations to rise, drawing the attention of the Science Patrol, who deployed a submarine into the lake to search for the cause but the massive monster managed to avoid their detection. However, Jirass came to the surface of the lake in view of two members of the Science Patrol that night, who were quickly in pursuit of its mad creator, who followed him to his house but were soon confronted by him, who refused to let them ruin his experiment and captured them. The next day, the massive Jiras finally rose from the depths of the lake and made his presence known. However, his master quickly attempted to prevent the Science Patrol from killing his pet and attempted to get Jirass to obey his commands, only for the man made abomination to trample him underfoot without a second thought as the Science Patrol tried both to stop Jirass and rescue their two captive members but their weapons did little more than anger the monster, prompting Hayata to call Ultraman into the fray. At first, Jiras attempted to intimidate Ultraman by throwing a rock into the air and destroying it with his electric ray, only for Ultraman to use his Specium Beam to do the same and outdo him. Ultraman and Jiras quickly began to fight but Ultraman managed to rip off Jiras's frill and used it to toy with the monster before continuing their fight. Try as it might, Jirass was little match for the hero and Ultraman used his hand to stab into the monster's side and soon, the beast bled from its mouth and collapsed dead to the ground.
Electric Beam: Jirass can emit an electric beam from his maw. This beam, while able to cause fires and blow up large boulders, isn't that strong.
Adept Swimmer: Jirass is a very good swimmer and can live underwater.