Wiki'd: 'schizophrenia,' 'bipolar disorder,' 'mental disorder'
This may be a bit complicated, so bear with me.
For a roleplay here on LiveJournal, I plan to apply for a character (Yako Katsuragi, from the anime/manga Majin Tantei Nōgami Neuro) but I am changing her history--making her into an Alternate Universe form of herself. The main issue if have with this is that the character has a rather... er, unique story. Rather than going into details, I'll make it simple.
Yako is the 'slave' of a demon who has come to Earth to solve the world's puzzles (i.e. mysteries, usually murders) and 'eat' them for energy. The demon forces her to come along with him, and pretend to be a great teen detective, acting as his cover to "solve" the mysteries for him so that he doesn't attract suspicion. She has a mystery of her own, though: her father was murdered, though it was ruled as a suicide because he was found dead in a locked room with no signs of forced entry and no clues to indicate another person.
Basically, the way that I want to spin this is that everything related to the demon--solving the mysteries, repeatedly meeting with the police department, etc.--was all in her head, caused by a mental disorder, the same that led her father to commit suicide. Her symptoms would be: hallucinations--visual and audial--about this demon; lost time when not around people she knows (I picture her wandering aimlessly around the city at these times, thinking that she is working on a mystery with the demon, ending up at the sites of various murders that are announced on television); and the false memories that make her believe that she has actually helped to "solve" these mysteries for the demon in her hallucinations.
*EDIT* I also wanted to add that in the anime/manga, it should be noted that Yako tends to stay calm in high-stress situations, and even though the demon physically abuses her (punching, kicking, hitting, etc.) she never shows signs of injury from these attacks. I thought that these may be clues to make the idea of a mental disorder more realistic.
I believe schizophrenia will suffice, but if there are any other mental disorders that fit her symptoms, then please let me know!