Hyakkaou Private Academy is an institution and the main setting in Kakegurui. It is a school were Yumeko, Ryota and Mary attends as well students from powerful families in the political and financial world.
Hyakkaou Private Academy was founded 122 years ago in Japan and is for many years since its inception, was a school were students from powerful families in the political and financial world attended. It is a school were students are not evaluated by studies or sports, but through the social status they posses. This is because those are not necessary for people who are destined to have power over others, which for them it is important to be well versed in tactics, reading and opponent and the strength to grasp victory which are abilities they have to prove and obtain through gambling.
2 years prior to the start of the series, a student changed the school tradition after winning a gamble from the former student council president. This causes the creation of the pet system. However, the discrimination of the school became stronger were the oppression increased strongly against those who are not good at gambling, and they became targets of bullying at the academy.
Gambling at Hyakkaou Private Academy is governed by the student council. It is known is that the student council members are using their powerful influence to collect money from students of Hyakkaou Private Academy. Payment of it is called a "donation", where it is optional but is practically obligatory. Hyakkaou Private Academy has a ranking system which can be given to students that have failed to donate to the school under 100 between 3,000 students or whom have accrued a massive debt that they cannot pay. Those students will be recognized as a "pet". If a student is a male, they will be called "dog" (pochi), if the student is a female, they will be called "cat" (mike). The hierarchy in Hyakkaou Private Academy is absolute were no student can go against it, and if they do, they will await the student council's reprisal. If the student wants to rid themselves of their "pet" status to, they have to donate but it will be impossible if the student has either a massive debt to pay off or no money to pay their way out of their status. The hierarchy is described as a perfect dead end which is known by the student as something that is extremely hard to escape.