Ok so when I was younger my cousin and I would watch a lot of like indie and random horror movies, but there’s one I very faintly remember but no one seems to know about. It involved this demon or monster, that I’m fairly certain was a girl, that would kill or possess people from air vents. I don’t remember any actors in particular either. But it definitely made me nervous for years to look up into air vents
Pee Chong Air (The Sisters) (2004)?
https://www.imdb.com/title/tt0450087/?ref_=fn_al_tt_1