The first one that pops to mind is Kanna37's Favourite Writer in the
It's a Dog's World collection. The collection and story we both rated MA. There is a T version on ff.n.
There are quite a few more that I've read, but titles aren't coming to mind. One had Kagome as the writer, and she dressed up as "The Lady of the West" from here series of books and her son finds her. There are also some that have Shippo and/or Souta as the writers (or mangaka) of the story.
I hope someone else recalls some of the other stories so I can reread too
