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. The book was written by the Master of Masters and, true to its name, contains the events of the future.

Kingdom Hearts χ
By using the power of his Gazing Eye 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 gifted the Keyblade to one of his apprentices, Luxu, instructing him to pass it down from generation to generation. The Gazing Eye would make and transmit back in 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.

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

To prevent this crisis, the foretellers established Unions to battle the darkness and used the Book of Prophecies to draw power from the future.

However, all but Gula's copy omitted 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. According to Gula, the "Lost Page" talks about the one who bears the Recusant's Sigil. Parts of this page are revealed by him to Skuld and Player when Ava confronts Luxu outside Daybreak Town:

Some time prior to the Keyblade War, the Master of Masters hands Ava a list with the five Dandelion Union leaders that eventually would succeed the foretellers after the war, circling one of their names in red to ensure that this one would get a copy of the Book of Prophecies. However, Ava reneges on the Master of Masters' orders in hopes of changing fate: she chooses Brain to receive the Book of Prophecies, who was not originally the one selected by the Master of Masters. Before parting with him, she places the list of names from the Master of Masters in Brain's copy of the Book of Prophecies, hoping that he would understand it when the time came to decide their future.

Kingdom Hearts Union χ[Cross]
Brain discovers that the Dandelions are trapped in a digital copy of Daybreak Town. Aware that Master Ava did not plan for this to happen, he resolves to act as a virus that will overwrite their grim fate, consulting the Book of Prophecies for answers. Brain takes the list of names from the book, believing that now is the right time.

Later, Ephemer discusses with the other Union leaders how Ava choose them, revealing that one of them was supposed to receive the Book of Prophecies. This in turn prompts Brain to reveal that he has a copy, much to Ephemer's surprise.

As the situation in Data-Daybreak Town escalates, Darkness reveals themselves to the Union leaders. They discover that the Master of Masters had written the Book of Prophecies and that Darkness had watched as it was written. In this manner, Darkness had learned that Ventus would harbor darkness in the future, prompting them to take Ventus as their vessel to infiltrate the Dandelions in the present.

Before Ventus, Lauriam, Elrena, and Brain leave for the real world, Brain gives the Book of Prophecies and the Master's Defender to Ephemer, informing his comrade that the he was meant to have them.

After Kingdom Hearts Union χ[Cross]
It is unknown where the Book of Prophecies went after it left Ephemer's possession, and the tome soon passed into legend. All the while, the Gazing Eye continued to bear witness to the future, allowing events to be written in the book ages prior.

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