Rei first appears in manga chapter 6 Love de kill tai (愛で殺したい, Ai de koroshitai?) and TV anime episode 3a The Handsome Shapeshifter Rei Appears! (変身美男レイが来た！, Henshin Binan Rei ga Kuta!?)). He comes to Earth to retrieve Lum. Moroboshi Ataru tries to convince Lum that she should go back with her own kind, but Lum lies and says that Ataru's child is in her belly, which infuriates Rei. He challenges Ataru to a potato eating contest and loses. This is the first and last time that someone out-gluttons Rei. In the next chapter Hatred nai bum/good-for-nothing (憎みきれないろくでなし, Nikumikire nai Rokudanashi?) (TV anime episode 3b Go away! Ladykiller! (くたばれ！イロ男！, Kutabare! Iro-otoko!?)) he continues to pester Lum about getting back together. Lum then agrees to do so but only if he can propose to her in Japanese. While looking at a cheat sheet he was able to, but Lum still refused, so he chased her and Ataru around town. This was the first and last time he was able to speak more than two words at a time.
Rei is the only character who surpasses Mendou Shuutarou as a ladykiller, but is quite dim-witted and a terrible glutton. Long ago both Lum and Ran were in love with him, but he got engaged to Lum, breaking Ran's heart. However, Rei's love for food and his shapechanging eventually caused Lum to call off the engagement. He follows Lum to Earth but eventually starts dating Ran, though he seems to be more interested in the food than Ran herself.
Powers and Abilities
- Shape shifting - Rei has the unique ability to transform into an Ushitora (牛虎, Cow-Tiger?). Whenever he sees food he becomes excited and transforms into his ushitora form.
- Lum: Rei was engaged to Lum before the start of the series, but she called it off. When he first arrives, he still is in love with Lum, and tries to get her back from Ataru. However, his interest in her eventually waned.
- Ran: Ran was in love with Rei, just as Lum was. When Rei was engaged to Lum, Ran's heart was broken, and she dedicated herself to revenge on Lum. Eventually, due to Lum having no interest at all in him, Ran decided to pursue Rei for herself, eventually getting him to fall for her.
- Kurama: Kurama fell for Rei while searching for a husband to replace Ataru. However, despite her Tengu servants' best efforts to hide it, she discovers his Ushitora form and is horrified.
Unlike the other Oni aliens, Rei usually only says a few words at a time.
- The creature comes from the Chinese compass (for which the directions have then names of animals) signifying the unlucky direction of the northeast. It is the direction from which oni are said to enter the human world, and that is why they are depicted as mighty, horned creatures wearing tiger skins.
- Rei in his cow-tiger form is featured in the 5000 yen bill in the anime version of Rumiko Takahashi's latest manga, Kyokai no Rinne.