Prez Koumori is the main character in the YouTube Series Yu-Gi-Oh! Excalibur. He also makes several appearances in another YouTube Series Yu-Gi-Oh Project Games
Prez learned how to play Duel Monsters from his whole family being related to the game, including his mother, father, brother and his uncle, Bandit Keith. Over the summer he takes residence in the country of Poland, where he is the national champion. He also has a secondary title as the Canadian champion for recently defeating Pedro. However, he prefers his title in Poland as his main identity. Ever since the incident of his family mysteriously disappearing, he started to grow more of a dark side, mostly for feeling isolated and alone, along with living with Bandit Keith, sharing a ruthless attitude. He still considers Paxton as his best friend, but Prez just recently came back to Wisconsin in the hopes of obtaining Excalibur, which he plans to use for restoring his family back to the way it was a year ago. After defeating Paxton in a test of dueling skill, he convinced himself that the only way to find Excalibur is to be unforgiving towards easy mistakes and to take cards from losing opponents. This strategy strengthens himself and eliminated the competition who search for Excalibur out of greed. This started in his third day of searching when he encounters Zack Pies in the forest road. Prez offers a bet to Zack in which if he wins on his first turn with no damage, he can take the opponent's card. If not, even with victory, the opponent can take his cards. Prez succeeded in the bet with a Great Maju Garzett combo, where he took Zack's Dark Armed Dragon. He eventually makes this a habit, where he uses this bet to defeat several opponents in his first turn and power his deck. This eliminated and weakened many duelists within the search.
Some time later, he began noticing a gang setting up base in his territory. He broken in and would have wrecked all of them, but one of them tells Prez about a duelist named Tom Elkmann, who possessed a God Card, Obelisk the Tormentor. Not wanting to miss up on the chance to take on a god, he searched out Tom Elkmann down in Illinois. When he finds him, they then duel. Both sides fight hard, but Prez eventually defeats Tom. Literally right afterwards, they team up in order to take on 2 members of the gang mentioned earlier and defeat them. Then, Prez heads on his way, expecting a rematch from Tom.
|Paxton LaBarge||1||No result|
|Maveric & Pedro Knauer||16-18||Draw (with Shawn Yuki)|
|Heartless & Camian||21||Win (with Paxton LaBarge)|
|Alternate Prez Koumori||30-31||Win|
Prez plays a DARK Devour Deck, based around monsters with powerful effects to bring instant kill/reinforce monsters.