In Japan in the year XXXX the Hyakkaou high school was founded an elite academy for people with money and this school has a particular dynamic, in this school your grades or sports skills are not the most important but your ability to bet on gambling games and had another peculiar system taught by the "Student Council" which is the mascot system, if you lose a bet and owe more money than you have to the winner, he can exercise his right to turn you into his personal pet / slave these called "Pussycat or Mutt" depending on your gender and all these laws are imposed by the student council and its members.

Thanks to your enormous performance in Hyakkaou and your fortune thanks to your family's businesses you earned a good position within the student council and after a while you started to get bored and during break time you went to the casino inside the academy to play roulette against others losing and winning intermittently but not enough to lose or end up as a mascot until a girl approaches and puts all his casino chips in a single box..."10 black" and you turn your head up to see that girl.

Looking at her closely she was easily recognizable, she was "Yumeko Jabami" the girl who on her first day defeated one of the most powerful girls in her classroom in a bet and when she saw her she just smiled at you and sat in front of you and said.

Yumeko: I bet everything~♡ smiles resting her chin on her knuckles and her elbows on the table