Brain

Brain is a Keyblade wielder who appears in Kingdom Hearts Union χ. He is a member of the Dandelions and was chosen by the Master of Masters to lead a Union after the Keyblade War. Like the other new Union leaders, he was given a book with laws set by Master Ava.

Before Kingdom Hearts Union χ[Cross]
Brain is chosen by the Keyblade and awakens within Daybreak Town, where he joins a Union of fellow Keyblade wielders. Eventually, he is approached by Ava and informed of the coming end of the world, then subsequently joining the Dandelions, and receiving training in preparation for crossing Worldlines in order to avoid taking part in the Keyblade War, thus ensuring the survival of light.

Brain meets with Ava on the hill overlooking Daybreak Town, where she asks him to become a Union leader. Though Brain initially believes that he's not cut out to be leader, he changes his mind after hearing that the Master of Masters was the one to choose the Union leaders. Brain becomes suspicious when Ava informs him that she can't reveal the other four leaders just yet, and so Ava poses a question to him: what if the world's fate was already decided. Extrapolating, Ava points 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, Ava 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. Ava 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]
As per Ava's instructions, the new Union leaders are to come together in the Keyblade Graveyard following the Keyblade War. Brain is the fourth to arrive, after Ephemer, Skuld, and Ventus, though he is surprised to see that he is not the last. Brain questions if the rules set forth by Ava are absolute, expressing his wariness to trust Ava because she wants them to lie to the Dandelions about the Keyblade War. Thinking of how had suffered, Ephemer states that no one else should have to carry the burden of the past, a sentiment Skuld and the others accept.

After the final Union leader, Lauriam, arrives, the Union leaders go to Daybreak Town and enter the Foretellers' Chamber, where Brain finds a copy of the Book of Prophecies and starts flipping through it. When Skuld proposes that they begin choosing which Union each of them will lead, Ephemer recommends that they maintain the Union χ in order to prevent the conflicts of the past world, with the other Union leaders agreeing to reconstitute the old system later as stated in the rules. Brain then suggests that, while the Dandelions are reliving the events of the past, they collect the necessary ingredients to create new Spirits and sends Ephemer, Skuld, and Ventus to collect the ingredients while he and Lauriam stay behind to make the necessary preparations.

Ephemer calls a meeting in order to discuss the Shift Pride, but when Lauriam doesn't make an appearance, Brain informs the group that Lauriam was attending a personal matter and had informed him that, whatever the circumstances may be, he'd side with Ephemer. Continuing, Ephemer mentions that the Rule Book states that they are meant to impose the Shift Pride, which Brain notes is essentially like a friendly contest between wielders, which Brain is decidedly in favor of. Meanwhile, Ventus and Skuld oppose the Shift Pride, not wanting wielders to raise their Keyblades against one another again. Ephemer finalizes the Shift Pride by voting in favor of it, explaining that he'd been inspired by a conversation with Lauriam to utilize the data of the Keyblade wielders which exists in the data versions of the worlds they visit ever since the Keyblade War. Given his conversation with Lauriam, Ephemer also mentions that Lauriam had been searching for someone who should have become a Dandelion, but he has yet to see them, being the reason why he'd sought to search the data for this person. With this in mind, Brain suggests that they don't pry, as it seemed like something Lauriam wants to pursue on his own.

When Lauriam returns, he asks Skuld about Strelitzia, given that Strelitzia's friend, Elrena's, Chirithy had last seen Strelitzia going into the same house Skuld had visited prior to her disappearance. Though nothing much comes from their exchange, Lauriam assumes that Strelitzia might have chased after the unknown individual she was pursuing and gotten herself caught up in the Keyblade War after all. Brain notes this as being odd, as Strelitzia was pursuing this individual in order to get them to join the Dandelions, but they had not done so before the bells tolled, meaning that they likely fought in the Keyblade War. This reminds Ephemer of Player, who was offered a place among the Dandelions, but ultimately declined and battled in the Keyblade War, and so Ephemer agrees to introduce Lauriam to Player. With Ephemer and Lauriam gone, Ventus asks why Brain's always spending so much of his time reading. To this, Brain explains that even if they overwrite the Keyblade War, the world is still on a destructive path, and thus Brain resolves to be the virus that overwrites that destiny.

Making his way to the Control Room, Brain encounters glitches and gets to work attempting to stop them. Ephemer, Ventus, and Player, whom Ephemer introduces, manage to catch up with Brain and question what's happening concerning the glitches outside. Brain reveals that he's managed to stop an infestation for now, before going on to explain how, in the world before the Keyblade War, they were able to visit worlds of the future via the Book of Prophecies. As these worlds currently existed, you did not require the Book of Prophecies to reach them, because they were all connected to Daybreak Town, though it would have been hard to reach them due to the scope of the world. However, since the Keyblade War, these worlds have become disconnected. Having been foretold, the worlds were recreated as data in order to ensure that they and their respective futures could still be accessed virtually, through the data Daybreak Town. When Brain poses the question of whether they are in the real or the data Daybreak Town, he notes that the presence of the glitches suggests that they are within the data version.

Reminding Ephemer that he'd mentioned Daybreak Town acted as a portal to the futures of worlds that already existed, Brain explains that they've since connected to a world that doesn't yet exist in their world or time. When this world connected to theirs is when the glitches started to appear, and though it was impossible for Brain to completely sever the connection, he has since managed to stabilize it, though they would have to investigate in order to fully understand what's going on. To this end, Ephemer volunteers, though Brains suggests their leader stay in case something goes wrong. Instead, Brain suggests that they send a Dandelion, and Player is quick to volunteer, despite the danger - though Ephemer remains resolute in going with Player. Admitting that it couldn't hurt, Brain agrees and opens a path to this new world for Player and Ephemer.

Ephemer soon returns alone, allowing Player to continue exploring the new world without him so that he could discuss what's going on with the other Union leaders. When Skuld and Lauriam arrive in the Control Room, Ephemer and Brain explain the situation and add that they'd pursued Darklings into this new world, and soon after enemies from their world began appearing in this new world, suggesting that the Darklings were responsible. Ventus mentions that they've also seen Noise of Ava's meeting with the Master of Master, while Lauriam mentions having seen Noise of Strelitzia as well. With all of the evidence presented, Brain concludes that they must be in the data Daybreak Town, causing Ephemer to ask whether or not there even was a real Daybreak Town, while Ventus wonders if it had been destroyed. Brain assesses that there is no way of knowing as they have been completely cut off from their original world, with no possible way of returning; suggesting this all to have been someone else's plan. And yet, still made good on his word to be the virus that overwrites everything.

Brain looks to the Book of Prophecies for answers, and is approached by Lauriam, who explains that he'd spoken with Elrena again, and learned that she'd known about the Keyblade War. Harkening back to when Brain had mentioned that it seemed odd that Strelitzia was hesitant to join the Dandelions, Lauriam reasons that she'd changed her mind because she'd learned something about the Keyblade War. Lauriam then suggests that Player also should have known about the Keyblade War, but something must have happened to cause him to change his mind about becoming a Dandelion, which is why Strelitzia sought him out in the first place. Needing time to think and believing that the time was right, Brain reads the memo Ava had left for him in the Book of Prophecies.

Afterwards, Brain summons his Chirithy and has him collect Ventus and Skuld for him, whilst he meets Ephemer on the hill overlooking Daybreak Town. Here, Brain tells Ephemer that only one of the five new Union leaders was supposed to have the Book of Prophecies, but he hasn't had to use the Book of Prophecies until now, as all the worlds were replicated in data as insurance. After having read Ava's memo, Brain realized that it wasn't meant to be him. Furthermore, Strelitzia was meant to be one of the new Union leaders and receive the book. Despite Ava having been the one who had changed who received the Book of Prophecies, Brain expresses that he doesn't believe it was her intention to change the new Union leaders. Beginning to believe that Darkness was pulling the strings. Chirithy, Ventus, and Skuld then arrive, and he asks them where Ava had told them she intended them to become Union leaders, and when Ventus reveals she'd done so near the clock tower, rather than on that very hill, Brain comes clean about how Ventus was never supposed to be one of the new Union leaders.

Then pushing for more information, he hears Ven further describe his encounter with Master Ava about being in dim light warehouse and leaving with the master. Believing his innocence knowing that Ventus never would've struck Strelitzia so cruelly but knowing that someone or something threw a problem into Ava's plans. He and Ephemer believed that Darkness posed as Master Ava, killed Strelitzia and gave Ventus her book. Seeing Ven grab his head in pain where he vaguely sees Strelitzia dying putting him under so much distress he comforted his friend and agreed with everyone in planning to tell Lauriam about his sister's intended role back at the clock tower.

After Ventus is put in his room to rest, Brain consults with Ephemer and Skuld about his innocence. Then concludes from Ventus' description that he was there when Strelitzia disappeared, but was unsure who or what planned this much out, with Ephemer believing it was Darkness.

Upon further discussing with Skuld and Ephemer, Brain believes now that Darkness is inside Ventus and will begin to come after them. They are then approached by an injured Lauriam, demanding answers about happened to his sister. Although Brain refused to give him an answer, Ventus enters the room and admits he killed Strelitzia, much to the others' protest. Brain tries to stop Lauriam afterwards Ventus collapses on the ground and Darkness emerges from him.

Design
Brain has gray eyes and black spiky hair, which droops down over his eye. He wears a black coat with rolled up sleeves, gold buttons, and a large collar, grey pants, black cowboy boots, and silver cross-shaped earrings. His face is initially concealed by a black fedora that sports a black feather with a tan streak down the middle.

Personality
Brain is cool, calm and mysterious. As noted by Ava and Skuld, Brain is clever, as shown as during the mystery of Strelitzia's death, having deduce Ava's intentions was to only change who received the Book of Prophecies, not the leaders who were chosen, and Ava would have wanted to make sure that Strelitzia was safe.

Like Ephemer, Brain was hesitant about becoming a Union leader, believing he was not capable of fulfilling the role, but resolves to perform his duties and prevent another Keyblade War from occurring.