The answer to this question is both yes and no. While the game of blackjack is certainly present in Kakegurui, it is not the primary focus of the series.
In fact, the game is only mentioned twice throughout the entire series, once in Episode 1 and again in Episode 10. In both instances, it is used as a plot point to illustrate how luck can play a significant role in life. .
In Episode 1, Yumemi mention that she has been practicing card counting in order to improve her chances of winning at blackjack. However, her count fails her when she plays against a professional gambler named Kazuya.
Kazuya effortlessly beats her by counting cards up to five ahead of Yumemi, which proves that even with careful preparation, luck can still play a significant role in one’s life.
In Episode 10, Kakegurui’s protagonist Saki tries out for a blackjack tournament held at the casino owned by Kazuya. Initially, Saki has little chance of winning due to her low playing strength and inexperience.
However, after befriending one of the casino’s regulars named Naozumi, Saki begins to learn the ropes of blackjack and eventually makes it into the tournament finals. In the end, Saki narrowly defeats her opponent by playing optimally based on her observations of Naozumi’s play style.
While Kakegurui does feature some scenes involving blackjack, it is not the primary focus of the series. Consequently, it is unclear whether or not players actually play the game in real life.
