Kotaro Higashi, an aspiring boxer with no relatives to rely on, joined ZAT. During the first battle, Kotaro's plane was hit, and sent crashing into the ground. Moved by this man's courage, the Ultra Brothers and the Mother of Ultra granted him a new life. The female hero placed his latest son, Ultraman Taro, into Kotaro. Not a second later, Ultraman Taro attacked Astromons. Taro attacked with many punches and kicks, until Astromons struck back with his acidic mist, allowing his to get multiple hits in. Taro managed to use the Storium Ray, however, the massive plant monster was destroyed for good.
The monster, Cosmo Liquid, attacks a construction site by a river in the outskirts of Tokyo. Investigating the case, Kotaro finds the monster and shoots it, but it mysteriously disappears. The monster has transformed itself into liquid and moved to central Tokyo along the flowing river. Kotaro transforms into Ultraman Taro and defeats Cosmo Liquid, which is swallowed into a mysterious pit that is rumored to devour anything. The next day, Kotaro himself accidentally gets swallowed by the pit. Hope is not lost, however, as Mother of Ultra is heading to Earth...