Seto in is the Yu-Gi-Oh! Forbidden Memories incarnation of Priest Seto. He is portrayed more as an antagonist, than his manga and anime counterparts. Seto is the high mage Heishin's right hand man and rival to the prince.
Seto Duel and defeated Jono at the Duel Grounds and proceeded to mock his Dueling skills. Jono claimed that Seto was not good enough to defeat one of his friends. He was unaware that the friend was secretly the prince. Seto postponed a Duel with the prince, as Heishin requested his presence. When he returned he was defeated by the prince, but then realized who he was.
After the Mages took control of the region, Seto found the prince at the Forbidden Ruins. He explained the meaning of a map the prince had found. It revealed the location of each Millennium Item. He advised the prince to defeat the High Mage at each of the shrines on the map. Although Sadin advises the prince not to trust Seto, he complied with Seto's instructions.
After the prince defeated one of the High Mages, Seto kidnapped Teana and held her hostage to draw the prince to him. When the prince and Jono arrived at the Dark Shrine to rescue her, Heishin ordered Seto to defeat the prince and take the Millennium Puzzle. Seto dragged Teana into a secret room, where he dueled the prince. Seto was defeated, but gloated about how the Mages do not stand a chance against the prince.
After the prince defeated the remaining High Mages and took their Millennium Items, Seto approached him and told him to go to the now unguarded Dark Shrine, where he could face Heishin. The prince complied and met there. Seto showed him the way to Heishin. After Heishin lost, Seto took the prince to the Forbidden Ruins, where he revealed his true plan. He had gotten the prince to gather all the Millennium Items and take them to the Forbidden Ruins. Now Seto could use them to acquire great power, by summoning DarkNite, but Heishin appeared and held a knife to Seto's neck demanding and demanded the prince to hand over the Millennium Items, under the threat of taking Seto's life. The prince gave Heishin the Items, which Heishin uses to summon DarkNite.
After the prince defeated DarkNite, Seto disappeared and was never heard from within the kingdom again.
The first time the prince faces Seto, his Deck contains many strong cards for such an early stage in the game, like "Gaia the Fierce Knight" and "Ushi Oni". The second time he is faced, he uses "Gate Guardian" and "Blue-eyes White Dragon". The third time faced, Seto uses many powerful cards, such as three copies of "Blue-eyes Ultimate Dragon".