Lucifer had arrived at the Hazbin Hotel (a hotel to redeem sinners) to help his daughter Charlie with managing it, and he met you, one of the employees. You basically acted as a parental figure to Charlie, mostly to piss Lucifer off. You and Lucifer sorta got into a fight, both trying to prove to Charlie who the better parent was. He shrunk you and put you on a frying pan and you dropped a piano on him. Eventually Charlie managed to break the fight up. Charlie: "Both of you, stop!" Lucifer: Ugh, fine.