Rei Batsubami is a member of the Hundred Devouring Families. In a past conflict, her family was banished from the clan by Kirari Momobami's family. Rei arrived to the Hyakkaou Private Academy, acting as a servant for the other members of her former clan and identifying as male with an androgynous appearance, while secretly planning to avenge Yumeko Jabami's sister. Rei is a character exclusive to the anime, and poses as an antagonist for the second season.
Rei is a biological teenage girl with a very androgynous appearance, having short light-brown hair with much longer styled bangs that cover the right side of her face, and empty dark-brown eyes. She wears white butler gloves with the standard male Hyakkaou Private Academy uniform; she also wears suspenders under her blazer. Rei seems to be the only member of her clan to wear glasses.
When she reveals her true self, she takes off her glasses, brushes her hair back with bangs that nearly cover her right eye, and multiple streaks which go around her head. She also opens up her blazer and removes her gloves revealing two tattoos that appear on the back of both of her hands. These tattoos are shaped like the "Bami" symbol crossed out. It is also shown that she no longer has empty dark eyes, which now have a lighter color and visible pupils.
After she was accepted back into the Hundred Devouring Families, she takes up a feminine appearance and wears the female uniform. Her hair is a bit twirlier now, she starts wearing pink lipstick, no longer has glasses, and her eyes don't appear empty anymore. In her hair, she wears the dragonfly brooch that she got from Yumeko Jabami's sister.
When Rei was younger, she used to have much longer hair with her bangs covering her right eye, and she wore a dark-blue dress with puffy sleeves. However, after Yumeko's sister suffered heavily at the hands of the Hundred Devouring Families, she cut her hair to the style she had during her debut.
Rei is a kind, helpful, polite and always serious person. While serving the other members of the clan, she often did not talk as she was nothing more a a servant to her distant cousins and only providing important information to others if they asked. Unlike most members of the family, Rei seems to be very sympathetic and compassionate toward others, which is demonstrated when Rei protects a "pet" girl who is bullied. Despite being serious, Rei is easily confused, especially when being praised or when someone is kind to her and does something nice for her due her essentially being treated as a object or servant by everyone around her since birth.
When she was a child serving as a house servant, Rei met a young girl who treated her very kindly — Yumeko Jabami's older sister, causing her for the first time to feel positive emotions due to someone complementing her and acknowledging her for the first time. But some time later, Yumeko's sister lost everything in the forced family civil war and became increasingly emaciated, which made Rei furious and raised her will to avenge her benefactor. It's the reason why she behaves very well with people, especially when it comes to the weak who are abused by others. She never really felt that she had a purpose in life except for helping others, and was always bound by these invisible chains to her clan. Rei also is very intelligent, having conceived the plan to become the head of the Hundred Devouring Families by subtly manipulating her cousins and taking advantage of them only seeing her as a object to plan behind their backs to her advantage. She eventually failed, but that experience has changed Rei, and at the end of the day she was free, confident, and happier with her life.
As a child, since Rei's family lost everything to the clan generations ago, she was treated as mere livestock and was essentially seen and treated as nothing more than a servant or object by her relatives. She was never acknowledged by others and had to clean, and serve them. But one day, Yumeko's sister came by the estate and gifted her a dragonfly brooch; she was the first one to treat Rei like a human. Whenever Rei saw her, she was happy. But one day, she was defeated by the clan as well, which caused Rei to become enraged, and cut her hair. At that moment she firmly decided to avenge her, and get back her place in the family.
Rei was the first to enter the Student Council room where she introduced the other Hundred Devouring Family members. She also explained why the Clan was there to the other Council members, and stated she came so that the others would have an excellent school life. Others would often invite her to gamble, but she declined every time. She also was the one to introduce Yumeko Jabami to the members of the family before a game. In spite of her role, Terano Totobami mentioned to Kirari Momobami that she brought Rei as insurance, and that she was her secret weapon. While with the other gamblers she didn't do much, Rei would sometimes walk around the school grounds, enjoying nature.
One time, she ran into two girls who were threatening a housepet. She kept the girl from hitting the Mittens and grabbed both of the bullies by their chin, remarking about how twisted gambling can make one. The girls were absolutely beguiled by her. She also brought Yumeko Jabami to the infirmary and treated her after she was poisoned by Miyo Inbami, practically saving her life. Later that day, Ryota Suzui thanked her for the second time. As they were talking, the housepet from earlier showed up with a bunch of cookies as a token of gratitude. Rei was really touched by this.
After Sumika Warakubami learned that Yumemi Yumemite bribed the audience, she told Rei to bribe them back, and Rei asked them to vote however they like. Later, she joined Terano and Yumi in watching the others play the Greater Good Game. Terano asked her whom she considered the best swindler, but Rei couldn't answer. When Yumeko talked with Kaede Manyuda about how she doesn't really feel remorse for others whose life she ruined by winning, Rei became angry and shouted at her, unable to understand how someone can be so heartless; Rei even referred to Yumeko's hospitalized sister who has fallen into despair. Terano told Rei to let off, so Rei apologized and went back to Terano. After the game, she informed the others of the bet between Itsuki Sumeragi and Terano, and announced Terano as the winner of this bet. Itsuki had to pay her 150 votes.
Rei was on her way to the broadcast center when she ran into the two bullies again and greeted them. They immediately blushed and ran off giggling. As she walked through the hallway, all the girls looked after her as she had become very popular amongst the student body. She saw a girl who had dropped her books, and quickly helped her. She then went to observe the broadcast announcing the current top runners of the election. Later, the Mittens girl whom Rei helped out, and another housepet offered to give her their votes, but Rei refused since it's against the rules.
After the incident at the Tower of Doors, Rei was responsible for the Hundred Votes Auction. Invitations were sent to the Student Council and a few others, but only a couple showed up. Rei then explained the game, saying that the sponsor of all the votes wanted to remain anonymous. The auction started, and Mary won votes in the first round. However, Rei was secretly participating as well. When Mary realized it, she called her out, and Rei agreed to stop. Yumeko was very excited about the whole thing, but also pointed out that there had to be other betters that they weren't able to see. Some of the Momobamis were, in fact, competing as well.
Suddenly, a myriad of Election observers entered with suitcases containing a total of three billion yen belonging to Yumeko, as she had asked them to bring her money to challenge Rei. Yumeko demanded to see her true self. After revealing that she arranged the auction, Rei threw away her glasses and "transformed" into her true self, revealing to be there for vengeance.
Rei actually got all the votes for the auction from all the students she helped. She set up a ballot box where they could put them, and acquired a tremendous amount of votes this way. The auction resumed and things were going smoothly. However, Yumeko figured out how to cheat the system and all the participants understood what she thought of: they each only bet one chip and won one hundred votes. Rei couldn't do anything about it and became angry and desperate. After she had no votes left, she sat on the floor, feeling completely destroyed. Midari Ikishima went up to her and grabbed Rei by the shirt, irritated by her behavior.
After Midari told Rei that the real gamble had not started yet, Yumeko came up to her and pointed to the three billion yen; she challenged Rei to one final gamble where they both bet everything (Yumeko bet her family name, and if she lost she would be reduced to livestock like Rei. Rei bet 3 billion yen). Although she was shocked by Yumeko's gambling addiction, Rei took up the courage and decided she finally wanted to break the chains that bind her. Rei accepted the challenge, inspired by Yumeko's sister's telling her that her heart belongs only to her. While everyone watched, Ririka Momobami tossed a coin. Yumeko won, but Kirari was so fascinated by Rei's actions that she deemed her worthy of the clan. Rei wrote down a new last name for herself and became a new person. For the first time, her life is actually her own.
- Gambling Women Again
- The Women Of Momobami Clan
- Do Not Touch This Woman
- Communicating Women
- The Connected Woman (non-speaking)
- The Hollywood Star
- The Treacherous Woman
- The Winning Woman
- The Woman By Her Side
- The Logical Woman
- The Woman Who Bears The X
- The Null Woman
- Rei is the first and only canonical genderfluid character.
- The kanji of the name Rei (零) means "zero" or "null".
- It also can mean "bell" (鈴), "beautiful, lovely" (麗) or "the tinkling of jade" (玲) with different kanji.
- The tattoos on Rei's hands are the reason why the second season is called Kakegurui XX.
- The "Batsu" in "Batsubami" refers to the X mark, which is often used in reference to a punishment game or a consequence as a result of losing.
- Presumably, Rei's new surname is Jabami — to honor Yumeko Jabami's sister, but this has yet to be confirmed officially.