In hell, demons get their power by extracting it from the fears of mortals. Led to believe by their overload Satan that being mean and scary will make their cesspool a better place for them. The most terrifying demons are given the job of breifly entering the human world using the Grimore and each demon is assigned an imp to help them train and prepare. However despite the fact that demons need human fear as a means of power, they can't necessarily touch them or get too close to them because of the humans known as exorcists who eliminate demons.
The best demon in the business is Alastor the radio demon and with help from his imp partner Moxxie, he surpasses all demons in the haunting position which puts him in a rivalry with the envious Vox. The two are close to be on top of the world but trouble arises when Alastor notices an open portal one night and decides to just grab a quick scare to amuse himself, only to make a startling discovery. The human girl at the house he's haunting is not afraid of him at all.
In fact she's fascinated by Alastor and actually tries to make friends with him. He panics and goes back to hell but forgets to close the portal. So the girl, called Charlie follows after him out of curiosity and accidentally gets stuck in hell which leads to extreme chaos when word gets out. Alastor and Moxxie end up having to hide her until further notice and try to figure out how to send her back to earth.
During her time with them, Charlie tries to teach Alastor and Moxxie that there is another way to live a happier life. By redeeming themselves and doing good. They both laugh at her idea but nevertheless she and Alastor do grow closer. They find that they both have a passion for music, singing, and dancing and the boys discover that Charlie's singing voice is actually more powerful than human fear. Which makes them wonder if human passion can be just as useful as fear.
But later on they make some other discoveries as well, like how Charlie arriving in hell being not entirely accidentally. And how Vox has been doing some secret planning.
If this ever gets made I think it would be super funny if Angel was George and Blitzo was George's partner Charlie. They're final running gag with the CDA could go like this.
Blitzo: 2319! We have a-"
Angel: (Grabs him by the throat) Not this time bitch!