Book of Prophecies

The Book of Prophecies (予知書) is a book that appears in Kingdom Hearts χ and Kingdom Hearts Union χ. It is the source of and s, which allow  to harness powers from the future.

Kingdom Hearts χ
By using the power he installed into the No Name Keyblade, the Master of Masters wrote the Book of Prophecies which foretold the events that would lead up to the Keyblade War and what came after. He then placed his Gazing Eye in the Keyblade and gifted it to one of his apprentices, Luxu, in order for it to make and transmit back through time the observations which would compose the Book in the first place. In order to prevent undue temporal paradoxes, he did not give Luxu a copy of the Book. Instead, he gave copies to his five other apprentices, who became the foretellers, with all but Gula's omitting the "Lost Page" (ロストページ) which covered the events of the betrayal of the foretellers, and how the Keyblade War would begin.

After reviewing the manuscript, the foretellers discovered the shocking final entry, which prophesied:

To avert this crisis, the foretellers established Unions to battle the darkness and used the Book of Prophecies to draw power from the future. Player's Chirithy later informs them of its creator's actions so they can understand the source of their power.

According to Gula, the "Lost Page" talks about the one who bears the sigil. Parts of it are revealed by him to Skuld and Player when Ava confronts Luxu outside Daybreak Town.

When the Master of Masters handed Ava a list with the five Dandelion Union leaders that eventually would succeed the foretellers after the Keyblade War, he encircled one of their names red to ensure this one would get a copy of the Book of Prophecies, along with the rulebook all five would receive.

Wanting to change the fate of many when it was time to meet with Brain on the hill overlooking Daybreak Town, where she asks him to become a Union leader. She poses a question to him: what if the world's fate was already decided. Brain already knows she's referring to the Book of Prophecies, asking what would happen if you could change what was written within it, with Brain wondering if the Book would change as well. Ava explains that there's no way of knowing, which means there would be a future that was not planned out. Thus, she provides Brain a copy of the Book of Prophecies, going against the predetermined future, as he'd not been chosen by the Master of Masters to receive it. Before parting with him she then places the memo from the Master of Masters in Brain's copy of the Book of Prophecies, intending for him to read it when the time came to decide their futures, hoping that her message to Brain would be clear at that time.

Kingdom Hearts Union χ[Cross]
After the Keyblade War was done as the new Union leaders entered the Clock Tower a copy of the Book was found and Brain starts flipping through it. To start off their duties as the new leaders he finds a page about new species of dream eaters called Spirits that can help Chirithies banish nightmares from their masters. To do so, Brain sends Ephemer, Skuld, and Ventus to collect the necessary ingredients to create them while he and Lauriam stay behind to make the necessary preparations.

Meanwhile as time went on Brain continuously read through the book, which didn't go unnoticed by Ven, from it he believed that they were still on a destructive path, even if the Keyblade War was overwritten, with that Brain closes the book and resolves to be the virus that overwrites that destiny.

Kingdom Hearts Re:coded
Following their defeat in the Datascape, Maleficent and Pete discuss the ancient Book of Prophecies. According to legend, it is capable of transcribing and conjuring future events, as well as creating entire worlds filled with beings and powers that have yet to exist. Maleficent decides to search for a connection between the Book of Prophecies and the Datascape, and she wonders if the Book is also connected to Jiminy's Journal.

Kingdom Hearts III
Maleficent searches for the Book of Prophecies in every world she can think of, believing the Book is locked away in the black box.

Notes and references
Livre des Prophéties Buch der Prophezeiungen Libro de las Profecías