Hi there! Because superhero fiction is such a niche category, we don't have a special place for it carved out on our Genre Map. Having said that, though, it doesn't mean you can't find a place for it on Book Country!
You are right: a fantasy subgenre is your best bet. Since superhero fiction originates in comic books, comic fantasy might be a good fit. Contemporary fantasy is another great option. Take a look at the genre descriptions, and they will help you decide where to shelve your book on BC.
I think it's still a good idea to mention in your About the Book that it is a piece of superhero fiction!
Hope this helps. Happy reading and reviewing!
Book Country Coordinator
--edited by Nevena Georgieva on 10/3/2013, 2:53 PM--