BOOKS OF THE ASCENSION. Buffyverse Term/Concept/Idea/Intratext.
In "Enemies" a harmless, horned demon offers to sell Buffy and Faith The Books of the Ascension, which he describes as "very powerful works and I'm not talking about the prose. They deal with some, ah, dark stuff. And the Mayor would hate for somebody to get ahold before he, ah, well you know." Faith later kills the demon and takes the Books to her new employer, The Mayor.
In "Choices," Willow manages to steal a page from the manuscript while The Mayor's hostage, which provides the Scooby Gang information that helps them formulate a plan to defeat The Mayor's Ascension at the Sunnydale High Graduation.