someone here on the forum released an app recently: Immersion Reader - E-Reader & Dictionary App
you will need to convert the kindle book to epub, but that’s fairly easy to do. (amazon doesn’t like it, but it’s not illegal as long as you don’t share the ebook.) bookwalker is more difficult in that regard.
also, one more thing I forgot: a lot of light novels started as webnovels and are often times still available on those sites. That’s a completely free and legal resource as well.
I hope you find something that works for you. 
