I'm looking for a short story I read a couple of years back. It was told from the point of view of an old cat, who has spent his life fighting demons[?] that try to come through weak places in reality. The demons need to possess a living being in order to do any damage, so places high in the sky used to be no danger but now are sometimes enclosed in sky scrapers. The cat is gearing up for his last fight, to protect the child of his humans.
It ends with something about the child playing with/learning from the cat's spirit in a mote of sunlight.
It is definitely not the Neil Gaiman story about the demon fighting cat. At first I thought it was in the anthology Magicats!, but I checked today, and it definitely is not. I think I first read it some time in the early '00s, but it had the feel of something that could have been written quite a while earlier.
Any guesses are much appreciated!