Itsuki Sumeragi is a supporting character in Kakegurui. She's a first-year student belonging to the "flower" class at Hyakkaou Private Academy and a member of the Student Council. Her father is the president of a prominent toy company in Japan.
She wears the Hyakkaou Private Academy issued uniform; a red blazer with black trim around the cuffs and collar that is decorated with gold buttons, underneath she wears a white button up with a black tie as well as a pleated skirt with black stockings that have silver stars on the sides of them along with a pair of brown loafers with black soles. She has blue eyes and blonde hair that comes down to her chin and bangs that reach her eyebrows. She has a green hairband in her hair. She also has pink painted nails with star-like decorations on them. In the manga, her nails are decorated with the suit of clubs.
Itsuki uses her gambling skills as well as the daughter of the president of a toy company utilizes her wealth to her advantage in order to get whatever it is she desires, whether it be a seat within the student council or even her collection of painted human nails. Equally as manipulative as she is business savvy, Itsuki uses her gambling match against Yumeko Jabami to promote her family's latest product while hiding her own secret that the cards she uses are rigged with temperature-sensitive technology that leaves her undefeated at her own game until Yumeko uncovers the truth of her deception.
Kakegurui - Compulsive Gambler
Following Saotome Mary's defeat at the hands of Yumeko, the student council members hear about this news. One of which was a current member of the student council, Itsuki Sumeragi, who with her riches as the daughter of the largest toy company in Japan, got the position. Itsuki showed excitement in trying to gamble with Yumeko.
During lunch time, Itsuki immediately followed Yumeko's trail in the school and somehow managed to get to her. She invites her to gamble with her, and while Suzui tries to halt Yumeko from gambling, she still wanted to gamble and accepts Itsuki's gamble invite. She invites her to play a game of "Double Concentration" in which the rules are fairly simple. 2 decks of cards will be used, making the total card usage of each game 104. Each player must then flip 2 cards of their choice in their turn. If they flip a pair of matching cards with the same suit and number, then they gain 2 points and the flipped cards are remained flipped open. If they flip cards that don't exactly match, then they lose a turn to the opponent. For example: You get a pair of 9 of Hearts and 9 of Spades, then they don't count as a matching pair. But a matching pair would be 2 4 of Clubs or 2 6 of Diamonds. For their match, Itsuki places down 20 irregular colored chips which are worth 1 million yen each, making it a total of 20 million yen. For the betting, Itsuki uses all the 20 million worth chips, making their bet 20 million. Though Yumeko says she does not have the money, Itsuki assures her worries by saying she'll lend her 20 million.
Then, they begin the game of "Double Concentration".