Spin-off of Kakegurui focusing on Midari Ikishima and her past.

A prequel to Kakegurui is set a year before the main story's events, and is centered around Saotome Mary.
Saotome, a bright young girl born into an ordinary family, has passed her transfer examinations and has started to attend Hyakkaou Private Academy. It's an elite school with an exquisite twist - gambling has become a central part of the school's rules. Saotome adapts quickly to the school's outlandish system, and soon succumbs to the gambling mania that she comes to be known for.

Yuuto Shiba is a 29-year old who, despite his desire to be a barrister, is a complete failure of a man. In a fit of drunkenness, he gets hit by a truck and dies. In the afterlife, he is brought into the world of Luanolde, and is tasked with implementing Japanese law into the country's court systems.

Hyakkaou Private Academy. An institution for the privileged with a very peculiar curriculum. You see, when you're the sons and daughters of the wealthiest of the wealthy, it's not athletic prowess or book smarts that keep you ahead. It's reading your opponent, the art of the deal. What better way to hone those skills than with a rigorous curriculum of gambling? At Hyakkaou Private Academy, the winners live like kings, and the losers are put through the wringer. But when Yumeko Jabami enrolls, she's gonna teach these kids what a high roller really looks like!

(Source: Yen Press)

Sakai Hiroaki is a high school teenage mastermind with a genius-level intelligence and a lack of interest in anything that is easy to him. During one unlucky day, in an attempt to stop a student from committing suicide, he ends up committing suicide himself. After he awakens, he finds himself not in the real world, nor in heaven, but in purgatory, along with a group of others who did the same. Sakai discovers that he and his peers are subjected to never-ending intense death games in this world for reasons unknown to him, and he tries to find a way to escape.

(Source: MU)