Let's call this place the Fight Club Tower for simplicity. The building itself is cylindrical, standing tall, with around 10 to 12 floors. The first floor serves as a gathering spot for spectators, where people come to check the day's fight schedule and place their bets on upcoming matches.
The rules of the Fight Club are straightforward: combatants must fight without armor, without weapons, and without any detectable use of Mana. They can only rely on what their bodies naturally possess, which gives a distinct advantage to demons with built-in weapons like claws or massive horns. Victory is determined by knocking out your opponent, forcing them to submit, outlasting them until they give up, or, if it comes to it, killing them.