Well.. For me I've been using this app called fan fiction reader... (It is the brown one) where you can read and download many fics though... (I've got 500 stories downloaded Hahahha in various pairings and shows)
It is pretty reliable even though you must use the search function to find the stories cause sometimes the browse function isn't working for less fics in other shows..
You can read it once you download it offline and it does not give up much space xD
All of the stories there are only available in fanfiction.com..
Hope this helps you