These characters below are all characters, which have no confirmed name yet and they aren't very important to the story.
Hana class' Teacher
She is the teacher of the Hana class, which Yumeko Jabami, Ryota Suzui, Mary Saotome and Itsuki Sumeragi belong to. She introduced Yumeko as the new exchange student and assigned Ryota to give her a tour around the new school.
They have to check that there is no cheating during the election gambles. There is at least one of them observing every game. The important ones are Rumia Uru and Inaho Yamato. They are distinguishable by their animal hoodies, which are based on the one that Runa Yomozuki constantly wears. A lot of them appeared after Yumeko asked them to bring her 3 billion yen in suitcases. The vice-president is called Ruri Fuen.
These two girls tried to force a housepet into purposefully losing a gamble with them. As she refuses, one of them wants to slap her, only to be stopped by Rei Batsubami and she lets the Mittens go. At first the bullies are angry, but Rei calms them and they are absolutely breath-taken by her charm as they were blushing while looking at Rei, unaware that Rei is actually a girl yet. They are later seen again blushing as Rei passes by and greets them. They, along with others then give Rei their votes.
They cheer at every one of her concerts. The president of their fanclub is called Shinnouji. Yumemi knows everything about them, but is secretly disgusted. After that secret is revealed, her fans are shocked, but still love her. Yumemi is touched and thanks them and they continue to cheer her on during every performance. During the election they gave her all of their votes. But even they are awed by the song of Kawaru Natari. Yumemi bribed them, but so did Kawaru, thus they voted for her. At the end of the battle, they motivated Yumemi, telling her that she doesn't need to be an actress and all of them cheered for her.
When Jun Kiwatari was trying to make Yumeko Jabami strip, they were eager to see that event. They then also stopped Ryoma from intervening. But when Midari Ikishima came, they were scared, that they would get into trouble. But she creeped them out, so they quickly flew the scene. Later they discussed, how the entire Student council are like manga characters. Now that Jun is a housepet, they probably torment him.
Back when Mary Saotome was thriving as a gambler, they followed and admired her. They also cheated for her during most occasions. As soon as she became a housepet, they treated her terrible. After she recovered, they were embarrassed how they acted and said, they were sorry. Their names are (Picture 3; from right to left) Anzu (the black-haired girl with pigtails and glasses), Midori (the murky-brown long haired girl) and Aruka (the short brown-haired girl). During the election, Rin Obami uses them for his own plan. He acted towards them like each of them was his special one. They all fell in love with Rin, but were heartbroken, when they found out he just used them for his selfish goals. During the War game they first played with him, but then conspired against Rin, when Ririka revealed the truth. After Rin lost they mock him at first, but then he apologizes. They still arent quite satisfied, but he leaves them since they even earned some money.
This blonde girl was the former president who used to lead the Student Council. But not long after Kirari Momobami entered the school, she was beaten by her and lost her place as president. Although it is not certain, it is possible that she committed suicide by jumping out of the window after her loss.
Traditional Culture Club members
Yuriko Nishinotouin has employed these girls and thus saved them from becoming housepets. One of them hosts the game, while the others welcomes new guests. They all have piercings on their hand, which they use to cheat during Life or Death. One of them, who is the shuffler during Yumeko's game, is called Kumagusu.
He is Kaede Manyuda's father and an important figure in his life. He was very strict and made it clear to his son, that he must be strong and powerful, in order to rule over others. If Kaede doesn't succeed, he would become worthless, as he puts it. This has shaped Kaede into who he is today.
Mary Saotome's father and mother. They are briefly mentioned in Kakegurui Twin after Mary meets Tsuzura Hanatemari again and recalls an episode from her childhood. When Tsuzura had a birthday party, they gave Mary a lot of money to buy her an expensive treat, knowing that her family was rich and had many connections. Even as a child, Mary felt disgusted by their attempt to ingratiate themselves with wealthy people.
A group of delinquents led by Kurimu Terasumi that caused issues around the academy (such as occupying classes). It's composed of a girl with straight, long hair; a girl wearing her hair in a messy ponytail; a tall guy with short, light hair; a guy with black hair and a light streak wearing a sweater instead of his jacket.
These two guys corner Nanami Tsubomi in the mens bathroom and want to force her to gamble against them, but lose on purpose so they can get her vote. They even organized a referee, since losing on purpose can't really be tracked and doesn't break rules, as long as everyone agrees to play. The goal of the bullies was to sell their votes to Terano, who currently buys them for 5 million Yen each. They get mad at Nanami when she refuses and want to get violent. However Yumeko interrupts them and challenges all of them to a gamble. They are too intimitated to bet all they have, so they leave.
This whole scene seems to be inspired by the scene where another housepet gets harrassed and saved. Since that event only happened in the anime, the manga most likely referenced it.
This girl plays Rock-Paper-Scissors against Jueri Arukibi. It is unknown if she also cheats, but she appears to be surprised by Jueri's actions during the game. She appears to play a somewhat important role in the live-action movie. This characters is also notably portrayed by Enako, a very famous cosplayer.
Manga Club members
They are members of the Manga Research Club. During the treasure hunt against Sakura Miharutaki, Mary and her friends come here to find a hint. The girl with the braids greets them and wants to help them, is unsure of what exactly theyre trying to find at first. Mary then does find the hint and they leave.