Ishiyama

Ishiyama was credited as a Great Sumo Slammers Warrior in Game Over with the ability to increase his size, durability, and strength.

Ben 10
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. 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.

He made a cameo in Monster Weather, where he was seen in a new episode.

Alien Force
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.

Ultimate Alien
Ishiyama starred in Sumo Slammers IV: The Movie in The Perfect Girlfriend, battling one of Kenko's minions in a sumo ring.

Omniverse
He only appeared as a video game character throughout the series.

In Rules of Engagement, he was used by Ben against Derrick W., under the name "Rob-H".

In Fight at the Museum, he was used by Exo-Skull with the username "Exo".

In It's a Mad, Mad, Mad Ben World: Part 1, he was used by Ben Prime against Ben 23.

Etymology
His name is Japanese for stone mountain.