Rulebook

The Rulebook (掟の書) is a book that appears in Kingdom Hearts Union χ. Every member of the Dandelions that is meant to become a Union leader received one copy from Ava, while the rules themselves were devised by the Master of Masters.

Story
To ensure the survival of light following the cataclysmic Keyblade War, the Master of Masters provided Ava with five Rulebooks intended to be given to five individuals whose inclusion in the Dandelions was integral, as they would succeed the Foretellers as Union leaders and utilize the Rulebook as a guide.

As Ephemer seeks to uncover the mysteries surrounding the Foretellers and the Book of Prophecies, he's approached by Ava, who reveals the imminent end of the world to him and asks that he help to ensure the survival of the light. Though uncertain about his role, Ephemer accepts and receives his Rulebook before being sent by Ava to a world made of dreams in order to prepare for the arrival of the other Dandelions.

With the Keyblade War approaching, Ava approaches Strelitzia after she witnesses Player's confrontation with Aced. Just as she had done with Ephemer, Ava informs Strelitzia about the coming events, providing her with a Rulebook. Although Strelitzia doubts her capability to lead a Union, she accepts her role - only to realize that Player is not a Dandelion. Strelitzia then sets out with her Chirithy, hoping to find Player and induct him into the Dandelions. During her search however, Strelitzia is struck down, and her Rulebook is stolen by an unknown assailant.

After the Keyblade War, as the Dandelions enter the new world, they lose all their memories and relive their experiences, though this time without the tragedy that befall the old world. When the time came for the Union leaders to gather in the Keyblade Graveyard, Brain and Ventus are initially reluctant to follow the Rulebook, as it instructed them to lying to the Dandelions concerning what they'd left behind. However, recalling the pain the Keyblade War caused Player, Ephemer and Skuld believe they should follow the Rulebook allow Keyblade wielders to be unburdened by the past.

Further discussion ensues when the five gather in the Foreteller's chamber, as they are meant to disband the Union χ put in place that allowed Dandelions from different Unions to intermingle. Not wanting to repeat history, Ephemer suggests that they leave the Union χ in place, rather than pitting the Dandelions against one another again. This would also allow them to discuss the Unions they will lead at length. Brain objects to this, citing the entry in the Rulebook, however Lauriam notes that the Rulebook does not refer to when they should disband the Union χ. With everyone in agreement, the Union Leaders proceed with their first task.

Eventually, Ephemer struggles with the Rulebook entry instructing the Union Leaders to institute a Shift Pride, which would pit the Dandelion against one another as a competition. While discussing the matter with Lauriam, Ephemer is reminded of the Dandelions' adventures in the worlds. Offering the subject of the Shift Pride up for a vote, Brain and Lauriam support Ephemer's decisions, winning out against Skuld and Ventus. Ephemer then brings everyone around when he reveals that he intends on accessing the data of the Dandelions from their adventures in the data worlds, meaning that that Dandelions would clash with the data rather than each other - once again preventing true conflict.