When Ben and Gwen were sucked into the Sumo Slammer Smackdown video game, he aided them in their progress. At first he believed Ben was his arch enemy, Kenko, the Shapeshifter, but was convinced otherwise by Gwen. He is very honorable, responding that "a sumo never cheats!" when Ben asks him if he knows any cheat codes to help them out, but decides to make an exception and show them a shortcut to the last level. He considered Gwen a far greater fighter than Ben; this may have been because of Ben's reckless efforts at impressing him as well as Ben accidentally costing him two of their life points. He and Gwen fought Kenko while Ben searched for the Upgrade token on the final level. Kenko took his last life, but Ben revived him as Upgrade. He declared that he found Grandpa Max, who joined them at the last minute and was little more than a rookie, to be the greatest warrior of all for knowing that cleansing Sumo salt would reveal Kenko's true form when he disguised himself to deceive Ben and Gwen. His name is Japanese for "stone mountain."
Ishiyama was mentioned in The Final Battle: Part 1 where Ben stated that his enemy Kenko teamed up with him in the Sumo Slammers sequel series, Sumo Slammers: Hero Generation.