Dixie Reynolds was a cheerleader and well on her way to becoming becoming a psychology student when she was old enough for college when in Dixie's sophomore year her older sister and a senior at the time was caught having an affair with a former mayor. The resulting two years of guilt by association directed at Dixie crushed any chance of being popular replaced by a reputation for promiscuity she didn't earn and even wore down her normally optimistic nature. The teasing and accusations finally driving her to attempt suicide via sleeping pills and vodka.
Coryphea would have made a pretty good shrink herself or possibly a cheerleader herself if she was allowed to directly interact with humans. When the war came she turns those skills to help keep up morale amongst her fellow rebels as she fought beside them. However when the age of wrath came and she and her fellow rebels were imprisoned she didn't have much chance or lifting spirits. When a mortal girl with a similar mindset to Coryphea's started dwindling and created an opening, the demon leaped at the chance and found her way to freedom.
They fight crime....
Not really. Getting shot sucks.
Once the possessed Dixie woke up she was immediately confused by the world around her, was she Dixie with an upgrade or Coryphea just driving the girl she never really could grasp. Initially getting her some time in a psych ward till she could at least sort her head out enough to get released. Her family long moved away to try and escape the further scandal she caused with her suicide attempt. Showing her past desire to help people keep their heads together Dixie got a job working for a suicide hotline using past experience to help relate. The newly released demon is otherwise trying to figure out the world around her with only a blur of memories to guide her.