When they gang first encountered Mai Kujaku, she's a conceited, laugh-your-head off duelist who's out for number one: herself. She's endlessly bragging and always trash talking, and she sometimes employs mind games to psych her opponents out. She enters the Duelist Kingdom Tournament strictly for the money at first, but the course of events will drastically change her outlook. It all starts when she duels Jonouchi. She thinks the novice will be a cakewalk, but with a little coaching from Yuugi, Joey actually manages to beat her. This doesn't sit well with Mai, and she manages to convince Rex Raptor to challenge him next on the provision that once he'd won, he'd get to duel Mai next. But amazingly, Jonouchi manages to show his own skills and beat Ryusaki all by himself.

The change in Mai's attitude starts when she loses her Star Chips to Panik (Player Killer): once of Pegasus' Eliminators. When Yuugi risks his life to defeat Panik and win back the Star Chips, she's at a loss to reply. She eventually leaves them, but not before leaving a terse note: "I owe you eight Star Chips." Mai takes time out to get her affairs in order. She's beginning to realize just how serious dueling can be, and she begins to come to Yuugi's aid. She was reluctant at first to chip in to help after Yuugi lost to Kaiba, but after Anzu went so far as to challenge Mai to a duel herself, she relents and gives him five Star Chips to make up for the ones he lost to Kaiba so he could enter the semifinals. But then, Yuugi learns he has to duel Mai… a much different Mai than before. This Mai had hardened into a truly serious duelist. The trash talk was still there, but underneath it all is a desire to see just what Yuugi was made of.

It's that serious Mai that convinces Yuugi to make amends with Yami, the spirit of the Millennium Puzzle, and once again work together to bring Mai a shocking defeat. But she takes the loss in stride. She realizes that she still has a way to go. But before she leaves, she does one more favor: giving Joey her entry card so he could face Bandit Keith (who stole Jonouchi's card). Jonouchi asked Mai if they were friends now, but she only answered to herself, "Dork, of course we're friends." Outside dueling, Mai has indeed become friends with Yuugi and the gang. She later helps them to rescue Kaiba from the virtual game trap, but more than anything, she's itching to see just how good she can be, hoping for another serious test so she can see just how she stacks up. She appears again later in the story and around the Battle City Tournament.