The Book of Prophecies (予知書 Yochi sho?) is a book that appears in Kingdom Hearts χ and Kingdom Hearts Unchained χ. It appears when travelling to another world and is the source of the cards and medals that are handed out by the Moogle in Kingdom Hearts χ and Kingdom Hearts Unchained χ respectively. These cards allow the player to use the power from the future.
Kingdom Hearts χ
According to Chirithy, before its creator disappeared, he bestowed his six followers with new names and gave five of them a tome from the Book of Prophecies. These five followers would become the Foretellers and read the future written in the tomes. One passage on the last page shocked them all:
The war in that place will lead to the defeat and destruction of the Light.Book of Prophecies
The World will be enveloped in eternal Darkness.
To save the world from destruction the Foretellers used the power hidden in book and handed it on to the followers of their respective Union.
However, in truth, the Master of Masters had planned to ensure the Keyblade War happens as foretold in the Book. To this end, not only did he give Gula another part of the Book of Prophecies, known as the Lost Page, but he also told Luxu the truth about the destruction that would be wreaked upon the world by the Keyblade War, a conflict which would erupt from the fighting of the separate Unions against one another. Luxu was given the task of overseeing these events to ensure that they took place as was foretold. This included possessing new vessels over the decades to ensure his task.
The Master additionally stored a different copy of the Book of Prophecies in a black box and made Luxu swear to never open it. He sinisterly told Luxu that he'd see why.
Kingdom Hearts Re:coded
Following their evacuation from the Datascape, Maleficent mentions to Pete about the ancient Book of Prophecies. According to a legend, it is said to be capable of transcribing events that have yet to take place, and even has the potential to conjure new things, creating entire worlds filled with beings and powers of those future events. Maleficent wants to search for a connection between the Book of Prophecies and the Datascape, even wondering if there is also a link between the book and Jiminy's Journal.
Kingdom Hearts III
Both Maleficent and the Organization search for the Black Box throughout various worlds prior to the Second Keyblade War, which Maleficent assumes a copy of the Book of Prophecies is contained within it.
The Book of Prophecies, as expected of its name, contains all of the futures foresaw by the Master of Masters, with one of them being the final page and the other called the Lost Page containing information on the instigation of the Keyblade War. The Book's contents is not just about the Prophecies, however, as the Master of Masters also wrote detailed information regarding many topics, including information pertaining to the Heartless and the Keyblade in general.