First Appearance: KINGDOM HEARTS Union X (2017)

Brain was appointed by Ava as one of five Union leaders to guide the Dandelions in the aftermath of the Keyblade War. Although initially reluctant, he appeared to change his mind upon discovering the Master of Masters was involved in making the decision. He is calm, cool and collected, never hesitating to speak his mind regardless of how others may receive his actions. 

Per Ava's instructions, Brain and the other leaders were not to meet until after the Keyblade War. He immediately took issue with it, likening it to that of a script that had already been written for them, such as in the Book of Prophecies. He believes the future should be unexpected, and that everyone should be able to decide their own fate. 

Seeing that resolve encouraged Ava to give Brain the Book of Prophecies. Between the pages where Brain's fate was enscribed, Ava hid the Master's note containing the names of the Union leaders and the one he wanted to receive the Book. These actions were intended to send a specific message, one she hoped that Brain would recognize when he finally opens the Book to those pages.

Brain comes to realize that the Dandelions' attempt to escape the Keyblade War had actually trapped them in the data world, which would soon suffer the same fate as the real one. He decides to investigate the backend in hopes of finding any clues that would help free them from their prison.