One of the many sources of inspiration for anime are light novels. What's an anime light novel? It's a short book, often less than 50,000 words long, which is often paired with anime illustrations. If these books are successful, they might be adapted into an anime. Though this is the case for most light novels, including Baccano!, Monogatari, and more, there are a few that are spin-offs of pre-existing properties - for example, Naruto has a whole series of these that focus on side characters like Shikamaru and Kakashi. A few, like Your Name by Makoto Shinkai, are even written concurrently with their anime adaptation, by the director themselves.
Which are the best anime light novels? There's plenty of amazing contenders - but the real answer is up to you.