Twin Tail is said to be a monster that lived in the Jurassic period. Twin Tail adeptly uses both tails for pounding attacks and to constrict enemies.

Twin Tail was found as a fossil-like egg during construction for an underground shopping mall by Jiro Sakata as he walked by. MAT Member Kishida mistakes it for just a normal rock, and the egg is buried back in the ground. However, moments later the egg turned giant and appeared above-ground. MAT set the egg on fire with their MN bomb but before the fire spread, yet failing and resulted in the egg hatching, as Twin Tail was born.

After that, Twin Tail fought against Ultraman Jack. During their fight, the Subterranean Monster Gudon appeared from below ground and the two monsters overpowered him. Twin Tail then ran away towards the sea to escape from Gudon as it is Twin Tail’s natural enemy.

Twin Tail reappeared near reclaimed land in Tokyo and MAT used a sleeping gas bomb to blind both of Twin Tail’s eyes. Now weakened, Gudon appeared from behind and bit Twin Tails' neck, killing the monster.