Chuck's Death Book
When I became Death, I inherited Death's Knowledge and Death's Library. And in Death's Library, everyone has a book. Even God.
Chuck's Death Book is a tome from Death's Library detailing how Chuck Shurley / God dies. As the incarnation of Death, Billie is the only one who can read it unless she gives someone else permission to read its contents. She says that Jack as well as Sam and Dean have a role to play in Chuck's death.
Unlike the other notebooks in Death's Library, this book appears as a black leather tome with the Greek symbols for Alpha and Omega on the cover. The book was retrieved by Sam and relocated to the Men of Letters Bunker.
Billie tells Castiel, Jack, and the Winchesters that God also has a book in Death's Library explaining how he dies. She explained that when Chuck started creating the universe, he decided to create a multiverse, however he needed to build himself into the framework of the multiversal quantum construct so the world would keep operating in his extended absence. In turn, he created his only weakness, that he would one day die just like everything else as Death prophesied to Dean during the Apocalypse 10 years prior in Chicago. When Castiel questions this, she reminds them that the books write themselves and that no one can read them unless she gives them permission. She reveals that Team Free Will 2.0 are the messengers of God's inevitable death.
Sam and Castiel recover the Key to Death from the Bunker's archives, allowing them to open a doorway to Death's Library. When Sam arrives, he discovers that the Cosmic Entity has been killing reapers, forcing them to summon Billie, but she's been ignoring them all. When it notices Sam, it teleports him in front of Billie's desk, pointing out that it already found Chuck's book.
It starts to torture Sam to call Billie's attention, but Sam lies and tells it that Billie sent him to retrieve the book, having her hands full with enacting the plan to kill Chuck. The Cosmic Entity questions whether Sam is lying or not, but he tells it that he can either take the book and they win or it kills him and they lose and the Cosmic Entity never goes back to sleep. Sam manages to leave Death's Library with Chuck's Book in hand.
- The Alpha and Omega Symbols appear on the cover of Chuck's Death Book. Alpha and Omega are the first and last letters of the Greek alphabet. In the Book of Revelation, it appears as a Christian symbol, serving as a title or self-designation for God. In Rabbinic literature, the word "emet" (truth), the first and last letters of the Hebrew alphabet, serve as the Seal of God and in Judaic tradition, it carries the same connotation as Alpha and Omega.