Been a lurking reader for some time. I have to say yours is the most unique "Azkaban Harry" story I have ever read, and I am charmed by the way you have brought it to this point. I hope it continues in the same approach.
The only real improvment I can see is th eneed to acquire a good Beta reader to catch the occasional word misuse or spelling error. Cause even Spell Check and Grammer Check on the computer, which would probably help, don't and won't catch them all.