Ben and Gwen are playing Sumo Slammer: Smackdown and Gwen is beating Ben at it. As a result, Ben takes Gwen's controller, makes her lose a life, then turns into Upgrade, merges with the computer and sets Gwen's score to 0. As Gwen tries to get Upgrade out, lightning hits the van's satellite dish and zaps them both into the game.
It's not long before they realize that all of the aliens in the Omnitrix are locked and they have to collect tokens in order to unlock them. On the way, Ben and Gwen find Ishiyama, the hero of the game. They must progress through the levels in order to get the Upgrade icon and allow them to leave the game, Ishiyama notifies them of a shortcut to the Sumo Slammer Arena. Ishiyama grows fond of Gwen while Ben feels left out and eventually started to do irrational things to get Ishiyama's attention which went against his will. However, as they get closer, the villain of the game named Kenko hears them and wants the Upgrade icon. The trio then deals with Kenko's minions. Gwen answers the riddle that is needed to proceed to level 13, but accidentally turns her body fat, like a sumo wrestler. She slams the ground and rides on the Dojo to level 13. At the arena, Gwen and Ishiyama fight off Kenko while Ben finds the Upgrade icon. Ishiyama loses his last life but suddenly reappears telling Ben and Gwen that he wants to go with them to the real world. Max shows to them that Kenko pretended to be Ishiyama. Kenko is defeated by Gwen and Ben. Finally, Ben uses Upgrade icon to become Upgrade and get him and Gwen out of the game. In the real world, the two run outside and play "real-world style" while Max plays the video game.