Beetlejuice au although this will have influences from other movies such as Edward Scissorhands, Casper, and Paranorman.
Adrien Agreste is a sweet, polite, kind, but lonely young man who lost his mother and despite being a devoted son, his father is abusive and neglectful toward him. One day his father does something that results in Adrien getting killed but he is so hurt and betrayed by what his father did that instead of moving on to the after life he comes back as a demon named Cat Noir who is the total opposite of who he was in life. He is rude, mischievous, crass, hot tempered, arrogant, and spends his time causing bad luck for the living. He soon proves to be such a problem that the council of the un dead run by Master Fu (He's basically the Juno of this fic) restrains him to the netherworld unless someone from the land of the living says his name three times in a row. However he can still sleaze around the house where he died.
Sometime after this Marinette and her overworking widowed father move into the old Agreste house. Marinette is considered strange and unusual by her classmates and even some adults because she has the ability to see and communicate with ghosts making her an outcast in school and a constant target for bullies such as Chloe the queen bee mean girl. Her only friends are Plagg and Tikki, the ghosts of a married couple who died but couldn't move on because they weren't ready. Cat Noir takes an interest in Marinette after learning that she's a lonely kid with no mother and a workaholic father just like he was in life and plots to trick her into saying his name three times but what he fails to understand is that while Marinette's father does work a lot he does love his daughter and actually tries to make time for her.