Guardian Angel Charles AU.
In this AU, Charles is a guardian angel who is meant to watch over his charges on Earth and keep them safe. He can only interfere in a limited way, something that frustrates him greatly. One day in 1989, during a regular check-in with one of his charges, who he had to rescue from being beaten by a group of boys, Charles senses a doorway to hell open briefly before closing.
Thinking that a demon had escaped hell, Charles summoned his blade and went to where he could sense the infernal presence. To his surprise, it wasn't a demon but a damned soul who had somehow escaped hell. He had intended to return it to hell. However, he stopped when he recognised the soul. It was Edwin Payne, a former charge of Charles, who he had failed in the most terrible way, and Edwin had been dragged to hell before he could intervene.
Knowing he couldn't banish someone innocent back to hell, Charles decides to try and help Edwin. However, he's unsure how to go about it. He watched Edwin in between his duties, wondering how exactly he could help Edwin. He couldn't just take Edwin to heaven, not whilst his soul was technically owned by hell. He also couldn't bring Death because although she could take Edwin on, he would just be taken back to hell.
In a reckless move, Charles pretends to be a psychic and introduced himself to Edwin. Despite being hesitant, Edwin soon found he enjoyed being around Charles. They soon began solving issues that other ghosts were facing, helping them to move on. Without Charles realising several years had passed however and they took on more complicated cases and the two became even closer. Throughout all of this, Charles kept his true nature to himself out of both fear and shame of what Edwin would think if he knew the truth.
However, soon, Edwin, of course, noticed things not least that Charles hadn't aged in a decade and never spoke of his past in detail. Charles would try to change the subject. However, Edwin kept asking. The choice would be taken away from Charles when he was forced to assume his true angelic form to fight a demon who had sensed Edwin and come to collect him. Edwin saw Charles glowing with colossal wings and his form glowing with celestial light and fire looking inhuman and horrific. Edwin runs, and Charles chases after trying to assure Edwin he would never harm him.
Soon, everything came out, and Edwin feels a deep sense of betrayal. Edwin doesn't blame Charles for him going to hell. However, in the past 10 years, he had trusted Charles with everything and told him things he had never told anyone. Charles, however, had lied about everything, and he didn't know if he could trust him again . Edwin didn't want to lose his only friend, so he does go back and try and rebuild trust. Charles promised that he would try never to lie to Edwin again, and they continued to help souls as much as they could, although with Edwin now fully knowing what Charles could do.
My god, I rambled in this, and I'm not even sure if it makes sense. Just an idea that came when I was watching the show again. I wish I had actual writing abilities because I would try to write a story, but this is the best I can do..