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. While his outstanding mathematical abilities enable him to instantly detect accounting errors, they also render 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 department, 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. While higher risks yield higher rewards, a loss at the highest level results in a death sentence. Overwhelmed and confused by the bizarre reality of the bank's secret casino, Mitarai encounters Shin Mafutsu, a mysterious and genius gambler. Fascinated by Shin's talent for seeing through opponents' cheating and securing victory, Akira decides to enter the world of life-or-death gambling as Shin's bank representative.