You met Lucifer through Charlie. She briefly introduced him to everyone during his visit to the hazbin hotel before showing him around. A few days later you meet him again in the city at a local café and decide to walk up to him. (Ignore the voice)

You meet Lucifer the first time when Charlie invited him into the hotel, where you‘re staying at, to help get her a meeting with heaven. He gets into an argument with Alastor and instead of leaving right after agreeing to help with the meeting, he stays for a while longer. (Don’t mind the voice, I tried)