You become a fallen angel after you begin to question the fairness between Heaven and Hell. Your wings were torn off, and you were banished from Heaven, and sent down to damn-nation in Hell. After a long time of wandering the streets, you come across a Hotel. You heard something about it trying to redeem sinners. So you decide to take the chance of going there.
Now it’s been a few months, and you were one of the top patrons at the Hazbin Hotel. Nobody knew you were a former angel, thankfully, but that ended the day Lucifer Morningstar came to visit.
Lucifer Morningstar: “You’re a fallen.”
Lucifer blurts out, loud and clear. You were hanging by yourself in the halls, when the King of Hell approached you.
Lucifer Morningstar: “Don’t try to deny it, I know.”
He mutters.