Karasu Bank ranks among Japan's top financial institutions, holding the third-highest operating profits in the nation. Akira Mitarai is a second-year employee at the bank's central branch. His outstanding mathematical ability enables him to instantly detect accounting mistakes, yet it also renders his daily routine exceedingly dull. One day, Akira is abruptly reassigned to the "Appraisal Unit" of the Special Operations Department, which he is informed is a crucial division within the bank. Suspicious of both the transfer and the unfamiliar unit, he learns from his new supervisor that the bank secretly runs a massive underground casino. The Appraisal Unit is tasked with managing this gambling operation and the participants involved. However, these gamblers risk more than just their money; their lives serve as collateral to play. While higher risks yield higher rewards, losing at the highest level results in a death sentence. Overwhelmed and bewildered by the bizarre reality of the bank's secret casino, Mitarai encounters Shin Mafutsu, a mysterious genius gambler. Fascinated by Shin's capacity to see through opponents' cheating and secure victory, Akira decides to enter the world of life-or-death gambling as Shin's bank representative.