Sennen no Yuraku is a Japanese novel of 170,446 characters, with 9,365 unique words and 1,905 different kanji. Its difficulty rating on Jiten is expert, 4.3 out of 5. The full vocabulary list ranks all 9,365 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.