i just thought of a Sashannarcy Haunted AU in which Anne is a regular human that is haunted by the ghost of her late friend Marcy (for reasons better not named).
Anyway, Anne finds a house real cheap and she moves in (with Marcy haunting her of course). The reason the house so cheap? It's also haunted!
By Sasha. And she doesn't take it well to Marcy's presence.
"wait, you can't scare here. This is my turf! Scoot off!"
And Marcy's like "well, as Anne's personal ghost slash demon, i go whenever Anne goes so that's it."
"... Hold on that thought. If Anne were to leave the house, YOU would leave with her?"
"Precisely"
And so they devise a plan to join forces and scare Anne's off the house.
Problem is, Anne is so used to Marcy's haunting that she's fear-free. In any case she pities Marcy and Sasha existence and she just brush off any attempt at haunting. It's "The Ghost of Canterville" with some "The Ghost and Molly McGee" sprinkled in.
Eventually Sasha gets used to the idea Anne would not move and just sits on the couch to watch soap operas with her and Marcy.