Offline furigana for iOS
You have several apps available on the App store now - just search for Furigana.

I have a friend that likes this one, but YMMV:


Furigana Reader - https://itunes.apple.com/us/app/furigana-reader/id529433422?mt=8


It does not work offline, so it doesn't meet your requirements unless you fail to find any offline software and can relax that constraint.