Kingdom Hearts χ Back Cover is a collection of HD cutscenes from Kingdom Hearts χ formatted into an hour-long movie. It is included with a package of games entitled Kingdom Hearts HD 2.8 Final Chapter Prologue.
Long ago in a period of time that would one day be referred to as the age of fairy tales, the Master of Masters wrote the Book of Prophecies, a book that detailed events that would one day come to pass. The Master gave a copy of the book to five of his apprentices, while he tasked the sixth apprentice named Luxu his role to watch over events to ensure that they came to fruition. To help accomplish his task, the Master bestowed Luxu a Keyblade known as The Gazing Eye, which contained the Master's "gazing" eye. While Luxu set out to fulfill his role, the Master would then give the remaining five apprentices unique roles as Foretellers; Ira was given the role to take over for the Master when the time came and to lead the other apprentices, Invi was given the role to watch over the other apprentices and report back to Ira, Aced was given the role to support Ira, Ava was given the role to prepare Keyblade wielders for the new world to come, and Gula was given the role to uncover the mysteries of the Book of Prophecies. Not long after the five were given their roles and formed their respective Unions as per the request of the Master, both Luxu and the Master disappeared without a trace.
Sometime later, Ira assembles the other Foretellers, informing them that there was a supposed traitor amongst them. To support his claim, Ira summons a captured dark Chirithy that he caught, which symbolized that its owner's heart had succumbed to darkness. While the Foretellers speculate who it belongs to, Ira claims that it had to belong to one of them, but Invi disagrees on his quick conclusion, causing Aced to question Ira on his position as the new leader. Aced, Gula, and Ava soon leave after this, while Invi stays and questions Ira on his unusual behavior. Ira explains that this incident involving a traitor wasn't mentioned in the Book of Prophecies, causing him to deduce that there was seemingly a Lost Page and that one of the other Foretellers possessed it. Invi ponders if it was part of the Master's plan to grant the Lost Page to only one of the Foretellers.
A few days later, Aced assembles Gula and Ava, where they express their concerns over Ira's leadership and his hastily concluded accusation of a traitor amongst them. Gula questions Aced on why he really assembled them, and Aced explains that he wants to form an alliance between their Unions. Aced goes on to explain that he believes that there really isn't a traitor, saying that the alliance wouldn't be to confront Ira, rather to combat the darkness. Gula and Ava support his overall goal, but Ava reminds Aced that forming alliances in their Unions were forbidden by the Master. Gula accepts the offer, telling that it was currently between him and Aced, much to Ava's shock, who wishes to continue following the Master's teachings. Aced respects Ava's beliefs, while Gula goes on to question Aced if Ira and Invi were aware of their plan. Aced tells him that Ira wasn't in on it but Invi was as the latter soon arrives. Invi questions what was going on, and Aced explains his proposition to form an alliance. However, Invi disagrees with his idea, reminding him that the Master forbade alliances in order to maintain power among the Unions and that any imbalance would lead to a desire for power and eventually darkness. Invi then accuses Aced of being tainted by darkness, much to the latter's anger, who questions her on her role to seemingly spy on the others and report back to Ira. Invi tells him that that was her role, but Aced tells her that it was to observe, not to disclose information to Ira. Aced then ponders aloud if Invi and Ira were scheming behind their backs.
Ava later goes to the fountain in the center of town, asking herself when the tension between the Foretellers will resolve. Ephemer soon walks by, asking if he could join her in sitting down. She accepts his request, and Ephemer asks Ava what was wrong. Ava simply tells him that is has been a "long day" before asking him if he remembers his question on why the Unions compete against each other as opposed to working together, shortly revealing to him that she too has been wondering that same question. Ephemer asks if it was because the Master said so, to which Ava agrees, saying it was something they must obey, as the Master said so. Ava then admits that she has begun to wonder, reminding Ephemer of his desire to look for answers and to solve the mysteries of the world. Ava tells Ephemer that she thinks that that is how things should be, how people should question things and think for themselves. Ephemer is surprised by this, telling Ava that she really isn't herself today, commenting that even Foretellers have their off days. Ephemer suggests that talking about the Book of Prophecies will cheer her up, but Ava tells him that there was no chance of that happening, much to the former's disappointment. Ava asks if Ephemer was trying to pull a fast one on her, much to Ephemer's embarrassment, saying that it was merely a joke. Ava continues, saying that she thinks it would be great if all the Unions could work together and be altogether friends. Ephemer reveals that he made a friend from another Union, saying that they weren't much of a talker and shy, and that they would meet again tomorrow. Ava tells Ephemer that it sounds like fun, telling him to go home and get some sleep. Ephemer agrees and begins to walk off, but not before telling Ava to cheer up. Ava thanks Ephemer before he continues on. Ava then continues to talk to herself, saying that if the worst happens, then she would be glad that she left the future to the kids that see the world in a way that she does. As a breeze of dandelions fly by, Ava tells them to let the wind carry them far, far away.
Meanwhile, Ira is reading the Book of Prophecies when Invi arrives. Ira asks if she has learned anything, to which Invi replies that it would seem that Aced and Gula's Unions have become allies. Ira says that Aced was the traitor all along, but Invi believes that he isn't. Ira questions why, with Invi explaining that Aced's means of unification was a way of gathering strength to oppose the darkness, saying that she believes that his heart still belongs to light. Ira reminds Invi that forming alliances were against the Master's wishes, which Invi acknowledges, saying that she will try to persuade Gula to dissolve the alliance with Aced. Ira offers to do it, but Invi insists that she do the talking, saying that his intervention will likely evoke more of Aced's anger. Ira agrees to let Invi talk things out, and she reveals that Aced has grown skeptical of the two of them. Invi explains that she will report less frequently as a precaution to avoid Aced getting any wrong ideas. Invi leaves, and Ira sits back down to continue reading the Book of Prophecies.
A few months later, Aced and Gula return to the meeting spot where they proposed their alliance. Gula tells Aced that he was done with the alliance, and Aced asks for what reason. Gula explains that the reason why he entered the alliance in the first place was to combat the impending darkness before saying that it hasn't come, furthermore explaining that there have been no incidents involving darkness recently and that Aced hasn't rallied anyone else to his cause. Aced tries to find a reason as to why, and in the moment Gula accidentally reveals that Invi agrees with the alliance dissolving. Aced questions if Invi told Gula to break the alliance, and with no way out, merely replies "maybe" before telling Aced that in the end he was the one who decided to do it for his previously mentioned statement. Angered, Aced grabs Gula, telling him that they still don't know who the traitor was while Gula says that that was exactly why. Aced releases Gula, and Gula tells Aced that he can't trust anyone but himself. Aced tries to explain to Gula that he wouldn't stand a chance against the darkness on his own, but Gula tells him that his mind is made up before walking away. Aced then exclaims that Invi will regret her actions.
A few more months later, Aced narrates that it has been a year since the Master's disappearance, saying to himself that it was time to fulfill his true role. Aced proceeds to engage Invi in a fight around Daybreak Town, asking her why she has to get in his way. Aced is able to disarm Invi, who proceeds to tell Aced that she is trying to protect the balance the Master told them to, telling Aced to come to his senses. Nearby, Gula is observing the conflict when Aced explains to Invi that if they do nothing, then the light will expire, and they will be unable to avoid the grim future that awaits them. Aced tells Invi that they need to defy the Master's orders in order to protect the world, causing Invi to question him if the Master was wrong in his teachings. Aced reminds her that the Master is no longer here, saying that he will not allow both the Master's prophecy to come true and the world to fall into darkness. Aced attacks Invi, but she is able to retrieve her Keyblade, using it to deflect his attack and knock Aced onto the ground. While Gula continues to observe, Ava arrives after following her Chirithy. Together, Ava and Gula confront Invi and Aced and question what was going on. Invi replies that she, regrettably, found the traitor. Ava tries to deny this, but Gula informs her that there is no time to lose before summoning his Keyblade. Ava reluctantly summons her Keyblade and points it towards Aced with Gula. Aced gets up, telling himself the Master's saying "may my heart be my guiding key". Aced soon lunges towards the three.
Returning to the now destroyed street, Gula leans against a wall in an alley holding a page, which is revealed to be the Lost Page missing from the Book of Prophecies. Putting away the page, Gula tells himself to trust no one but himself before walking out of the alley. Gula later returns to the meeting place, where he finds Aced leaning against a stack of chests panting. Gula asks Aced if he wants to find out what his role is before revealing that the books they were given were incomplete, telling Aced that there was a Lost Page. As Aced gets up, Gula explains that on the Lost Page was details of a traitor amongst the Foretellers before summoning his Keyblade, saying that the Master wanted him to find and stop the traitor. Aced tells Gula that he will never again consider him his comrade, telling him that it doesn't matter if he believes he is the traitor, berating Gula that the latter was fully aware of the presence of a traitor and watched as the Foretellers fought, saying that he will never forgive him. Aced begins to walk towards Gula before summoning his Keyblade. Ava soon arrives, where he sees Gula collapsing onto the ground. Ava stops Aced from finishing off Gula, and after a tense moment, Aced de-summons his Keyblade and decides to stumble away. Ava helps Gula up, asking why it had to come to this.
Aced soon stops to take a breath, where he finds Ira leaning against a nearby wall. Aced asks if Ira came to finish him off before collapsing on the ground, but Ira tells him otherwise. Ira explains that he wished to fulfill his role, telling Aced that is wasn't their place to try and change the events of the future. Ira reminds Aced that their mission is to ensure that the light lives on, saying that with only five lights, they could not afford to lose any. Aced questions if he still considered him one of the five light, to which Ira replies that he did. Aced commends Ira for being such a good guy after all the things the Foretellers have been through, saying that it was one of the reasons why he respected him so much. Ira soon helps Aced up, and Aced worries that there might still only be four lights, saying that Gula was using the knowledge of the Lost Page to apprehend the traitor, all while claiming it to be his role. While Aced struggles to stay on his feet, he continues on pondering what Gula's true intentions were, saying that the one thing he does know is that he will never forgive him for hiding the knowledge of a betrayal. Ira tells Aced that he will deal with the matter, telling him to keep it to himself before walking away, telling himself that he needs to see the Lost Page.
Later, Ava's Chirithy warns her of Ira's approach. Ava confronts Ira, asking what was wrong. Ira tells Ava that he knows Gula was nearby, but Ava tries to deny it. Ira asks where he was exactly, but Ava refuses, instead asking him what he was going to do. When Ira refused to give a clear answer, Ava tells Ira that she won't let him near Gula. Ira proceeds to walk away while Ava returns to Gula, informing him of Ira wanting to find him. Gula realizes that it has come to everyone wanting to know about the Lost Page, telling Ava of its importance and his role. Ava questions why he would tell her this, saying that she has enough to think about with keeping the Master's teachings and her own role. Gula comforts her, saying that she always walked the straight and narrow path, while he was a fool for basing his actions on the ambiguous Lost Page. Gula then reveals his intentions to summon Kingdom Hearts with the intention of drawing back the Master, saying that by breaking the rules can they bring him back. Gula continues, saying that if things remain the same, then all of the world was doomed to fall. Gula tells Ava that he needs enough Lux in order to go through with his plan, asking Ava to help him with the matter. Ava refuses, reminding him of the consequences that summoning Kingdom Hearts would have on the rest of the world. Gula soon gets up and staggers away, leaving Ava alone in their hiding place.
A few days later, Ava confronts Invi, asking her why she told Ira on where she was hiding Gula, saying that her actions could be making things worse than they already were. Invi asks why that should bother Ava, telling her that she still has her Union and has gathered the best Keyblade wielders from all of the Unions before accusing her of training them in a secret location. Ava reveals that that was her role, much to Invi's surprise, who apologizes for overstepping the matter. Ava apologizes too, saying that she shouldn't have snapped. After a moment, Invi asks what Ira wanted, but Ava responds that she doesn't know, saying that all Ira told her was to give up Gula, but Ava, fearing for Gula, refused to tell him of Gula's location. Invi asks how Gula was doing, but she responds she doesn't know where he went, except that he is on a mission to collect Lux. Invi concludes that that is the same reasoning why Ira and Aced are as well, saying that they are trying to maintain the balance, but not the one they were expected to keep. Invi realizes that if they are collecting light for themselves, then Keyblade wielders will turn against each other, which would lead to the Keyblade War. Ava laments that what was written in the Book of Prophecies was soon to come to fruition; light will expire. Ava asks Invi what she will do, with Invi explaining that she too will collect Lux, telling Ava to do the same in order to delay the inevitable.
Ava soon rallies her own separate faction, the Dandelions, revealing that war will soon rage, and that those who wish to protect the light will turn on their allies for the sake of their loyalty to their own Unions. Ava explains that while there will be no winner, and that while everything will be lost to darkness, the Danelions are the seeds of hope; they will not fight in the war, rather they will travel far away to the world outside. Ava reveals that their training was to prepare them for this task, saying that the future and light lay in their hands.
Much later, Luxu is seen wandering through the now barren Keyblade Graveyard with his Keyblade and a mysterious black box given to him by the Master. Stopping to look at his Keyblade, Luxu repeats the Master's saying "may my heart be my guiding key".