Random Dead Boy Detectives fanfic idea. Body Swap with consequences.
David is desperate to regain his influence over Crystal so he used a demon ritual which would create a spiritual inversion between him and Charles. David would became a ghost with Charles physical appearance whilst Charles would be forced to take on David pure demon form.
David attempts to gaslight Crystal whilst looking like Charles however since he's nothing like Charles they quite quickly discover what has happened and try to trap David with Iron however he has a backup plan as Charles is currently trapped in a demonic form in a magical circle designed to trap a demon.
Eventually they are able to find Charles and trap David and Edwin is able to find a spell which should switch them back. However something goes wrong and Charles spiritual body is destroyed along with David. David is dead however Charles is left a malevolent writhing mass of darkness (not sure what David looks like as a demon).
From here Charles would have to learn how to exist as a demon and eventually finding someone to possess. He has to adapt to not only more malicious instincts and new powers but also now others react to him. Even Edwin and Crystal are wary despite being able to hide it.
Not sure where you could go with this. Perhaps he could find a way to become human again or begin a spiral or corruption and darkness. You could go incredibly tragic with a peaceful afterlife forever beyond him. Edwin feeling terrible guilt because Charles only ever stayed for him. Crystal unable to be around Charles because beyond just knowing what he is she can sense it.














