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.
After Jack doesn't kill Chuck, the book's ending changes. Billie finds what it says "interesting" and suggests that it still involves Jack. The book is left in the Winchesters' possession, but they can't even open it as only Death can read it. When they do manage to get it open, they discover that it's blank -- the pages can only be read by the current incarnation of Death unless they give someone permission to read its contents. They use the book itself as part of a "Plan B" to lure Chuck out into the open so Jack could steal His powers and become the new God.
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.
Billie tells Dean that according to the book, her role is now over until the end and Dean must guide Jack the rest of the way instead.
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.
In exchange for bringing Jack back from the Empty, Billie demands the book back. Sam reluctantly hands it over and Billie reads the ending, stating that because Sam and Dean aborted the original plan, the ending has changed. Billie finds what it says interesting and after bringing Jack back, tries to take him with her as he will still be useful. However, Dean slashes Billie with Death's Scythe, forcing her to flee without Jack, the book or the scythe. Sam then attempts to read it himself, but discovers that he can't even open the book.
When the Winchesters bring the book to Michael, he tries and fails to open it. Later, Lucifer arrives at the Bunker claiming to be an emissary of the Cosmic Entity, having been brought back from the Empty to aid in the fight against God. He traps and kills a reaper named Betty to transform her into the new Death. She opens the book in private and later meets up at the library with the open book in hand. However, before Betty reveals what's on it, Lucifer kills her and takes the book, revealing that he was actually brought back by Chuck to take the book back from the Winchesters. After restraining the Winchesters, he offers Jack a chance to join him on "the winning team", but he is stabbed in the gut and killed by Michael with the archangel blade.
With the book's contents revealed, Sam takes the now-opened book and starts translating it from its obscure Enochian text using the Book of the Damned. He later finds a spell that has to be performed in a certain spot at a certain angle of the sun which should be powerful enough to find Chuck and destroy him. They perform the spell, but it quickly gets countered by Chuck, who reveals that Michael tipped him off due to jealousy towards Chuck for choosing Lucifer, his "new favorite", to recover the book. Michael tries to justify his actions as he ultimately sided against the Winchesters, but Chuck smites him and proceeds to beat Sam and Dean. After a while, they start laughing, revealing that everything was a trap designed to lure him out.
Chuck turns to Jack and tries to smite him, but Jack steals Chuck's powers, including Amara, and heals Sam and Dean. Sam passes Chuck his death book, but He finds that the pages are blank, since only Death can read its contents unless the current incarnation give someone permission to read from the pages. Sam says they'd made the same discovery, so they'd come up with a Plan B. They knew that Michael would deceive them and kept the truth hidden from him while enacting their true plan: turn Jack into the new God and render Chuck into a human. Ever since Jack exploded into a metaphysical supernova in the Empty, Jack has been absorbing life energy from the plant life around him. He also began absorbing celestial energy from the earlier battle against Lucifer and cosmic energy when Chuck used his powers to kill Michael and attack the Winchesters, making Jack unstoppable. Chuck expects them to kill him, but they decide not to give him a quick death or any glorious ending of any kind, rather condemning him to continue living life until he grows old and eventually dies, forgotten and unmourned by all. Jack and the Winchesters drive away in the Impala, leaving a traumatized Chuck behind, along with his blank death book.
- 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.