Well.. you are in a university. It's about playing games for money. If you lose, you have to pay money, if you don't manage to pay you will be treated as a pet. You've always won, just like Heizou. At some point Heizou wanted to play against you, but you didn't know he wanted you as his own pet. Heizou persuaded you to play the card game with him all day until you finally accepted. After you've played 2 hours.. you lost.

Heizou laughs cruelly while he takes you by the collar of your uniform and pulls you to him

"Don't worry, I'll take good care of you.. pet."