Cuphead is a game inspired by cartoons of the 1930s. Play as Cuphead or Mugman, battling debtors for money for the evil Devil. Why should Cuphead and Mugman have to be debt collectors for the Devil? At one time, two people went to the Devil's casino, and they kept winning. That's why the devil noticed two people.
The Devil has made an attractive bet. If two people win this bet, they will own the entire casino. If two people lose, the Devil will take both souls.
But unfortunately, in this bet, Cuphead and Mugman lose. That's why Cuphead and Mugman had to make a deal with the Devil: Find other debtors for it.