Rou Vuooru no Wakusei is a Japanese novel of 152,798 characters, with 9,607 unique words and 1,878 different kanji. Its difficulty rating on Jiten is hard, 3.7 out of 5. The full vocabulary list ranks all 9,607 words by how often they appear, and you can study them on Jiten or download them as an Anki deck.
Here are some of the words that appear most often in this media, as well as a sample of its rarer vocabulary.