Seeing as light novels are now acceptable criteria I guess (since they are all text except maybe 10 or so pictures amidst 120-240 pages of text), I highly recommend 狼と香辛料. The first series is done (18 novels long), and a new sequel series is currently being published. There is a decent amount of furigana, but the medieval setting and focus on economics means that the content can get pretty dense sometimes. I personally also enjoy it for the well-paced, adult romance that is so rare in the 高校-obsessed otaku industry.
To give a basic summary: MC, a traveling merchant, picks up a wolf girl previously worshiped as a deity for centuries and agrees to help get her to her home in return for her assistance in helping his trade. Lovingly nicknamed the Book of Economics by many readers, the plot itself is more focused on the money schemes the two find themselves in with the objective being more of the setting. As I mentioned above, there is a romantic element, too. It’s easily one of my favorites.