I’m always looking for things to do that are not work on my thesis, so the other day I wrote a script to take all of the books on Aozora Bunko and sort them by WK level. Here’s the result! For each book on Aozora, it tells you at what WK level you can read 80, 85, 90, and 95% of the unique kanji. (If people would be interested in a list that looks at percent of all kanji rather than unique kanji, I can probably make that happen too.) I hope this is useful! Link below.
Feel free to ask me any questions you have! I also recommend opening it in Excel (if your version of Excel supports Japanese characters) so you can sort it easily however you want to.