Hyakkaou Private Academy is a school for the privileged and influential, playing host to the children of businessmen and politicians. However, unlike other schools, students at Hyakkaou do not pride themselves on academic achievement. Instead, they value strategic prowess and the ability to read people. Come nightfall, many places on campus transform into gambling dens overseen by the student council, where players compete for rank, money, and more.
Ryouta Suzui spends his days as a "house pet"—a student ranked in the bottom one hundred, forced to serve his peers. His circumstances soon change when a mysterious new transfer student, Yumeko Jabami, arrives at the academy. Despite Suzui's warnings, Yumeko quickly becomes immersed in the school's gambling scene, facing off against several high-profile opponents. Her exploits draw the attention of the student council members, who start meddling in her affairs. Suzui tries his best to keep Yumeko out of trouble, but to his chagrin, she turns out to be the type of person best suited to attend Hyakkaou: a compulsive gambler.