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The World began in darkness. And from that darkness came light. From the light came the people, and the people had hearts. Evil burgeoned in those hearts, begetting more darkness. And the darkness spread across the World like a plague. The light, the symbol of the World's hope, was devoured by shadow. Leaving nothing but ruin... An utter failure. But, the first light—the light of Kingdom Hearts—it can give us a new start. An empty World, pure and bright...Master Xehanort
Kingdom Hearts is one of the major objects in the Kingdom Hearts universe. It is the heart of all worlds, and a source of great power and wisdom. It can be seen as the heart of everything. Due to its great significance, it has repeatedly been sought by the villains of the Kingdom Hearts series, in particular the series's main antagonist, Xehanort.
In the prequel Kingdom Hearts Birth by Sleep, set ten years before the events of the first game, Kingdom Hearts appears in a form similar to Kingdom Hearts II, but blue in the sky above the Keyblade Graveyard. The graveyard is all that remains of a conflict called the Keyblade War, set many years before Kingdom Hearts Birth by Sleep. Keyblade Masters affiliated with both Light and Darkness fought to create the legendary χ-blade, a Keyblade capable of unlocking Kingdom Hearts. The Keyblade Masters failed and destroyed themselves; all that remain are their weapons which litter the desolate world.
This χ-blade will open a door―one that leads to all worlds! Then, Keyblade-bearing warriors will flock here from each and every one of them, to battle for the light within Kingdom Hearts! And just like the legend says, the Keyblade War will begin!Ventus-Vanitas
Some time after, an aged Keyblade Master named Master Xehanort formulated a plan to create the χ-blade, intending to unlock Kingdom Hearts. In his reports, Xehanort explains his views of the equilibrium of Light and Darkness and how they countered those from Master Eraqus's. Opposite to Eraqus's beliefs of light being absolute, Xehanort saw that light could not exist without darkness. Xehanort believed that the balance between light and darkness was what sustained the worlds. However, he noticed that light was prevailing and that darkness was excluded too much. As a result, he created a goal for himself to destroy the current system of light and recreate a new system of darkness, and through the rise of darkness, he would reorganize the worlds.
Along with the χ-blade, Xehanort also needed one more ingredient in his plan: a vessel. With the opening of Kingdom Hearts, he would be able to obtain a new body and discard his old one. As a result, his search for the vessel led him to Terra. He saw that Terra was looking for power, and that through obtaining this power, his heart would also give birth to darkness. Thus, with this observation, Xehanort concluded that Terra was to be his new vessel.
At first, Xehanort's plans worked well, as he set the scene for his dreams to come into fruition. In the end, he succeeded in creating the χ-blade by way of manipulating his former apprentice, Ventus, and his dark counterpart, Vanitas. With the creation of the χ-blade, Xehanort stopped his battle with Terra, released his heart through striking his chest with his own Keyblade, and used the power of Kingdom Hearts to transfer his heart into Terra's body. However, after obtaining Terra's body, part of Terra's emotions went into the discarded armor, forming the Lingering Will. Xehanort lost to the Lingering Will in a battle and fainted, unable to continue his plans with Kingdom Hearts prior to his memories being sealed.
In the first game, Xehanort's Heartless, Ansem, Seeker of Darkness, and the horde of villains led by Maleficent sought out Kingdom Hearts. Both wanted to draw out the darkness that surrounded it in order to gain immeasurable power and knowledge.
To accomplish this, Maleficent searched for the Seven Princesses of Heart, the maidens that possessed hearts that had absolutely no darkness within them. When brought together, these princesses would reveal the Final Keyhole, the only way to Kingdom Hearts itself. Thus, Maleficent attacked many worlds with the Heartless in her pursuit of them, and managed to capture all seven. All the while, she was being used by Xehanort's Heartless, whose original self managed to discover the nature of hearts, as well as Kingdom Hearts itself.
At Hollow Bastion, what remained of Radiant Garden after the chaos Xehanort caused, the seven princesses were finally gathered, but only when Sora sacrificed himself to release Kairi's heart using a Keyblade constructed from the hearts of the six other princesses, was the path to Kingdom Hearts finally opened. With Xehanort's Heartless having gained possession of Riku's body and forcing Riku's heart to wander into the darkness, he disappeared behind the darkness that poured out from the keyhole on the way to Kingdom Hearts.
After Sora was restored from his Heartless self, he once again went to Hollow Bastion, and sealed the Keyhole made by the princesses, holding off the great darkness. Regardless, Xehanort's Heartless remained a threat, so Sora and company ventured to the End of the World, a place created out of the remains of the worlds taken by the Heartless. There, the Heartless thrived, and beyond it, in the endless abyss, lay the unlocked door to Kingdom Hearts.
After a long battle, Xehanort's wounded Heartless reached the endless abyss, where the Door to Darkness lay, with the Universe of Kingdom Hearts#Realm of Darknessm of Darkness and Kingdom Hearts waiting behind it. Xehanort's Heartless forced the door to open, hoping for Kingdom Hearts to fill him with the power of darkness. However, Kingdom Hearts was revealed not to be darkness, but light. The light overwhelmed him, destroying him. But even with his defeat, the darkness that surrounded Kingdom Hearts threatened to overwhelm the Universe of Kingdom Hearts#Realm of Lightm of Light, with Heartless flocking to it in droves. In order to stop the Heartless threat, Sora was forced to close the Door to Darkness, trapping Riku and King Mickey on the other side. Nonetheless, the sealing also restored the destroyed worlds, along with the barriers between them, while preventing billions of Heartless from invading the Realm of Light.
Throughout the entire game, Organization XIII is trying to collect Hearts by destroying Emblem Heartless, in order to create their own Kingdom Hearts within The World That Never Was. Though the Organization's members work towards that goal to become complete beings, Xemnas, Xehanort's Nobody, intended to become one with Kingdom Hearts itself. In one scene, Xemnas shows the other Organization members how big their Kingdom Hearts is from the top of the Alter of Naught, explaining how close they are to complete their plans. After this scene, the world can be seen outside the windows of The Grey Room or Organization members' bedrooms in Castle That Never Was as it slowly grows whilst Roxas and Xion gather hearts throughout most of the year.
Hear me, Kingdom Hearts! It seems we must begin anew. Ah, but know this: I will give to you as many hearts as it takes. Mark my words. You can no more be complete without me than I without you. Heed me, Kingdom Hearts! Lend me your power, so that we may be complete! The power to erase the fools that hinder us!Xemnas
After Xion's demise and Roxas' reunion with Sora, Xemnas alters his scheme for himself and the remaining Organization XIII members to use Sora in destroying the Emblem Heartless so they can reap the benefits and become whole. When Sora learns of this plot, however, the Kingdom Hearts above the Castle That Never Was had grown to an enormous size. Xemnas aside, a revived Maleficent also seeks out Kingdom Hearts once more and refuses to let the Organization get to it first.
But due to Ansem the Wise's attempt to seal Kingdom Hearts away with a digital encoder, the explosion that sent him to the Dark Margin and restored Riku's original form left a giant hole in Kingdom Hearts, causing countless hearts to rain down over the world, becoming Heartless as soon as they touch the darkness that emanates from the city, with other Nobodies, mainly Dusks, attempting to catch the falling hearts to complete themselves. With Kingdom Hearts damaged, Xemnas attempted to have the Keyblade wielders help him all over again, though their refusal forces him to take drastic action to carry out his plan of becoming one with Kingdom Hearts.
Thankfully, a new door, much like the Door to Darkness, appears, allowing Sora and his companions to enter Kingdom Hearts as well. But Xemnas had already absorbed Kingdom Hearts' power, and attempts to use it against his opponents after transforming Kingdom Hearts' dimension into a replica of the World That Never Was. Though he tries his best, and nearly defeats them, the combined efforts of Sora and his friends bring about his downfall. What ultimately happens to Kingdom Hearts after Xemnas's defeat is unknown, but it can be presumed that the Kingdom Hearts Xemnas created using hearts Sora released with his Keyblade no longer exists.
Kingdom Hearts 3D: Dream Drop Distance
The artificial Kingdom Hearts created by the former Organization XIII can be seen in the skies above Riku's portion of The World That Never Was.
Upon his return, Master Xehanort reveals to Mickey and Riku his plans to start another Keyblade War using the thirteen darknesses comprising the real Organization XIII and the seven hearts of light comprising the Seven Guardians of Light to forge the true χ-blade and open Kingdom Hearts.
Kingdom Hearts III
Upon creating twelve of the thirteen dark pieces needed to complete the χ-blade, Master Xehanort summons the true Kingdom Hearts in the skies above the Keyblade Graveyard with his Keyblade. After striking down Kairi in order to force Sora to attack him, the resulting clash between the two creates the final dark piece, allowing Master Xehanort to complete the χ-blade and open Kingdom Hearts, tainting it with his darkness as it expands over the world. However, the guardians of light devise a plan to push Master Xehanort into a place between time and space while they focused on containing Kingdom Hearts from the outside. While Sora, Donald and Goofy force Master Xehanort into Scala ad Caelum to defeat him, the remaining guardians stay behind to keep Kingdom Hearts at bay.
During the final battle, Master Xehanort uses the χ-blade to summon Kingdom Hearts, using its power of light to combat Sora and company. However, Master Xehanort is ultimately defeated, and weakly reveals his plan to start a purge with Kingdom Hearts, which would result in the world being reset. However, the rest of the guardians arrive to reveal that Kingdom Hearts was closing on the other side, and the heart of Master Eraqus emerges from Terra's heart to convince Master Xehanort to surrender the χ-blade to Sora. After Eraqus and Xehanort pass on and ascend to Kingdom Hearts, Sora uses the χ-blade to seal Kingdom Hearts.
- In the mosaic above the door to Kingdom Hearts, a Hidden Mickey insignia can be seen.
- According to Nomura in Director's Secret Report XIII, it is implied that the differing colors of Kingdom Hearts is due to the nature of its assemblage. The Kingdom Hearts made by Organization XIII was assembled from the "hearts of men," meaning the hearts of people, turned into Heartless, were compiled into it. In Kingdom Hearts Birth by Sleep, the χ-blade unlocked Kingdom Hearts from "the hearts of worlds," meaning the hearts of entire worlds were assembled for its creation.