There is a large selection of Japanese light novels that are being translated into English. This is where a lot of the original source material for anime comes from. The anime is often created to sell the books, in fact.

There's a lot of stuff that won't be appropriate until they hit 13yo or so, but my nephew, a voracious reader, started reading LNs around 10.

Spice & Wolf is a personal favorite that might be a good fit. They will miss out on the romantic subplot but that's only a small part of the story