Yukio was visiting his relatives the Yanos when a fisherman brought in a Mutant tadpole for examination. After his visit, he was seen again in a nightclub where his love interest Miki Fujiyama was singing. The club was evacuated when some of Hedorah's sludge seeped into the lounge, and while in Yukio's car, he and Miki saw Hedorah and Godzilla preparing to fight. They stay and watch Godzilla ward the Smog Monster off, and the next day they take the Yanos to the place where they saw the monsters fighting to allow Toru to collect some samples. In Toru's laboratory, he was able to identify the long term effects of Hedorah's presence and explain them to Yukio and Miki. The next day, Yukio took Ken and Miki to an amusement park, where Ken fears he saw Godzilla. Yukio assured him that no monsters would come on such a nice day, but he was quickly proven wrong. On their way home from the park, Yukio and Miki were attacked by Hedorah, and only barely managed to escape. Yukio then plans to host a party on top of Mount Fuji in order to rebel against Hedorah. The celebration was cut short when Hedorah and Godzilla arrived to fight. Yukio then led a charge against Hedorah in which he encouraged the party-goers to throw torches at the monster, an act that led to his and their deaths.
Yukio Keuchi was portrayed by actor Toshio Shiba, who is also known for portraying the character Koji Kasuga in Silver Kamen.