Dimitri, known as Kagurazaka in Japanese, is a Ra Yellow student who tends to mimic other people's Decks, impersonating the owner of the Deck in almost every detail.
His appearance mimics Yugi - he has similar, but smaller bangs that fall over his face, his jacket flares out from the waist just like Yugi's did and the patch on his shirt bears the shape of the Millennium Puzzle. When impersonating Jaden, he uses Jaden's Slifer Red wardrobe and even styles his hair in a similar albeit messier fashion.
His personality changes depending on who he is impersonating. Dimitri could be a jab to the phenomenon of netdecking and Cookie Cutter Decks, as he attempts to win Duels by copying the strategies and mannerisms of known professional Duelists is very similar.
In the dub, Dimitri mimics Yugi's voice when he uses Yugi's Deck. He also refers to his Spell Cards as "Magic Cards", as this was the term used in the original Yu-Gi-Oh! series before the revised printing format of the TCG took effect. Also during his turns, the Duel score from the original series is played as opposed to the GX score.
Dimitri is first seen trying to get a ticket to see Yugi Muto's Deck on display by Dueling Syrus Truesdale for the last one with Syrus trying to get it for Jaden Yuki as he already had one. After losing a Duel against Syrus Truesdale with a copy of Dr. Crowler's Deck, he got desperate because he had researched the strategies of many strong Duelist such as Yugi Muto, Seto Kaiba, Zane Truesdale and Dr. Crowler while still unable to win Duels, so he decided to steal Yugi's Deck from its display case during the exhibition.
He successfully does so late at night and believes that he will become all-powerful with this Deck. When Syrus caught him with the Deck outside on the rocky harbor area, Dimitri duels him to test out the power of Yugi's Deck. Dimitri defeats Syrus, and Jaden then challenges Dimitri to get the stolen Deck back. During the Duel he actually manages to convince himself that he is Yugi. In the Japanese version this happened towards the end of his Duel with Jaden, while in the English dub it happened beforehand. Despite having the Deck in his possession, Dimitri is defeated by Jaden with the explanation to him being that he lacked the same heart that Yugi put into creating his Deck. Apparently, the message doesn't get through, as he then goes on to impersonate Jaden. In both the English and Japanese versions, he proceeds to mess up Jaden's signature pose and catchphrases, though said phrases differ between the two.
He made a cameo in episode 179 watching Jaden's Graduation ceremony in his original clothing.
Dimitri lacks an original Deck of his own and is seen playing Crowler's "Ancient Gear" Deck and Yugi Muto's stolen Deck. However in both versions, he makes a quick reference to having used Seto Kaiba's (likely excluding any Blue Eyes monsters, as in the continuity, only Kaiba possesses Blue Eyes White Dragon) and Zane Truesdale's Decks. After his final loss, he made a Deck resembling Jaden's.
Dimitri steals Yugi's Deck, which was displayed in a special room within Duel Academy, and uses it in two Duels to "test" its strength. The Deck focused on retrained "Chaos" versions of Yugi's "Chaos" Ritual monsters.
When first faced in his event, Dimitri uses Immortal Magicians, which utilizes a lot of Yugi's cards from the anime. After said event, he resolves to be more original with his Decks, and rotates periodically between an Ancient Gear Deck, an improved Spellcaster Deck, and an Exodia Deck (after you complete the game, he does not use the Ancient Gear Deck anymore).