Rei sneaked into Duel Academy masquerading as a boy seeking Ryo who she had a crush on. At one point she blushes seeing Judai take his shirt off. Judai catches her sneaking into Ryo's room. Seeing Ryo and two other students enter and while running Rei's hat and hairpin fall off revealing her longer hair causing Judai to realize that she is a girl.
Later Rei calls Judai outside to ask why he didn't turn her in. He asks her why it had to be a secret. She didn't answer so he suggests that they duel. She asks that he remains silent if she wins. She meets Ryo after the duel but he turns her down because of how young she is. Since she is too young to attend the school she has to leave. On leaving her crush shifts from Ryo to Judai much to his surprise.
Rei returns in the second season during the Genex Tournament. She challenges Ryo but he declined and she duels Jun Manjome instead. While she didn't win she is allowed to enroll in the school. The academy is later transported to another dimension. Rei is poisoned after being attacked by Yubel (via a possessed student) and Judai is among the students who go get medicine from a submarine to save her.
During the Darkness arc there is a tag team tournament. She notices that Judai and Asuka are not getting along so she adds the trap card Partner Change to her deck just before the duel. With it, she can switch places with an opponent if the opponent agrees. Asuka agrees allowing Rei to be on Judai's team. But when Judai and Asuka recoil Asuka destroys Partner Change returning them to their original teams.
Charmershipping is a less common shippings, but has some very devoted fans. Supports felt that both Judai and Rei were energetic and would get along. It rivals Fiancéeshipping.
- This ship gets it's name from Rei's first deck that used Maiden in Love and Cupid Kiss to "charm" Judai's monsters taking control of them.