A regional finalist who specializes in dinosaur monsters, Ryuzaki (Rex Raptor in the English dub) is a duelist who appears on the boat to Duelist Kingdom. He hits on Mai and invites her into his private room. She makes a bet with him– if she beats him in a duel, he will clear out of the room for the rest of the trip. Mai easily beats Ryuzaki and happily kicks him out.
Later on in Duelist Kingdom, he demands a rematch from Mai, but she only agrees to duel him again if he can defeat Jonouchi for her. Jonouchi beats Ryuzaki and wins his Red Eyes Black Dragon.
Ryuzaki and Haga both appear in Battle City but neither get very far.