One of the main protagonists, and a powerful Vanguard player who attends Hitsue High School. Kai only likes to battle strong players, and dislikes those who run away or cannot back up their boasts with skill. He battles with a Kagero deck with his ace cards being Dragonic Overlord and later Dragonic Overlord the End. He has a few trademark quirks when fighting, such as adding "the" to his move declarations (e.g. - "Stand up! THE vanguard" and "Check THE drive trigger!") and declaring "Final Turn" when he is confident he will win by the end of the current turn.