Editing Heart

[[File:The King's Memory 01 KHII.png|thumb|right|220px|Hearts held captive in Ansem the Wise's laboratory.]]

The primary meaning for "heart" in the ''Kingdom Hearts'' setting does not refer to the physical organ, <ref>'''''Kingdom Hearts III''', '''Vexen:''' How does he do it? A creature absent a heart, and yet able to exist. Not even my finest replica can do that. [...] THIS is all they meant by "heart"? We've been chasing the wrong box!</ref>but instead to a metaphysical animating force. What actually makes up a heart is a mystery to virtually everyone in the setting,<ref>'''''[[Kingdom Hearts II]]''''', '''Ansem:''' "We may profess to know the heart, but its essence is beyond our reach."</ref> leading many characters to devote themselves to researching the heart to unlock its mysteries. However, this research helped demolish the barriers between worlds, setting up the events for the first Heartless invasion and causing many worlds to be plunged into darkness.

As of yet, it has been determined by the various characters that the heart is primarily made up of [[light]] and [[darkness]], the latter of which formed due to people's greed. The exceptions to this are the [[Princesses of Heart]], maidens whose hearts are free of darkness, and hearts artificially made devoid of light or darkness, such as [[Ventus]] and [[Vanitas]]. Additionally, [[Dr. Finkelstein]] attempted to create an artificial heart for the purpose of making the [[Heartless]] more terrifying, rather than pursuing knowledge. He believed that the key elements of the heart are memories and surprise so his [[Dr. Finkelstein's ingredients|ingredients]] contained the essence of these two components. However, when [[Oogie Boogie]] consumed the heart that the doctor had created, it had an underwhelming effect. Oogie Boogie's plan was to control the Heartless by taking the heart, but few Heartless answered his call. This indicates that Dr. Finkelstein's hypothesis about hearts is incorrect, reinforcing the mystery surrounding hearts. Later, the [[real Organization XIII]] also attempt to create an artificial heart by collecting data of both positive and negative emotions on a program chip and installing it in [[Baymax 1.0]]. [[Vanitas]] states that his heart of pure darkness was restored by the Organization using the negative emotions collected by Monsters, Inc. Both suggest that hearts are constructed from emotions.

The heart appears to be responsible for the composure of memories, will, goals, and ambitions, as is the case in the transfer of [[Master Xehanort]]'s heart into [[Terra]] and the internal struggle of wills inside [[Terra-Xehanort]]. Despite lacking a heart, Nobodies inherit these traits from their original selves. The heart is also responsible for emotions, as beings lacking one, such as the Nobodies, cannot feel emotions.

According to legend, the χ-blade shattered into twenty pieces, seven of which were of light. These seven pieces then became hearts of pure light. The bearers of these hearts are known as "Princesses of Heart," because they are always female, for reasons unknown. Because they are needed to access Kingdom Hearts, the Princesses were sought by selfish and villainous beings who wished to rule all the worlds; [[Maleficent]] and [[Master Xehanort]] in particular. Kingdom Hearts could only be accessed by the completion of a Keyhole, which required all seven pure hearts to be joined as one in the [[Keyblade of heart]]. These hearts were released, however, due to Sora keeping Kingdom Hearts out of the villains' reach.

Hearts are also able to merge with others or be split, as seen when both [[Xehanort]] and [[Eraqus]] join hearts with Terra, and when Ventus's heart merges with Sora's. A much later instance of this would be Kairi's heart merging with Sora's during his first journey. They can be split to produce an embodiment of either the light or the darkness, as seen when Master Xehanort produces Vanitas by unlocking the darkness of Ventus's heart. There are notable differences when hearts merge based on the intentions of said hearts' owner: Ventus and Kairi left their hearts with Sora for safekeeping, unintentionally giving him access to a Keyblade and Kairi's memories, respectively. However, if someone merges their heart with the heart of another against their will, the victim will take on traits from the invading heart's original owner, as shown with [[Terra-Xehanort]]. In a similar scenario, if someone places a fragment of their heart into another, it can gradually turn the victim into a clone of the original person (though, in the case of Master Xehanort, his heart is strong and full of darkness, so it corrupts the host regardless if they are willing or unwilling).  

In ''Kingdom Hearts III'', the members of the Organization, minus [[Ansem, Seeker of Darkness]], [[Xemnas]], [[Young Xehanort]], and [[Vanitas]] (who already had hearts filled with darkness) did not turn into clones of Xehanort after receiving pieces of [[Master Xehanort]]'s heart; instead, they only gain his golden eyes and pointed ears. Even after their defeats, remnants of their hearts lingered on as copies of Master Xehanort in a unique new uniform; they later merged with him to create a powerful [[Keyblade Armor]].

Hearts removed from their bodies, but not transformed into Heartless, lose some of the limitations of a physical form. In addition to being able to enter other peoples' bodies, they can move through time itself, as long as a version of themselves is there to greet them, as revealed in ''Kingdom Hearts 3D: Dream Drop Distance''; as Master Xehanort, Riku, and Ventus exist in the future, Young Xehanort could bring Ansem, Xemnas, Riku Replica, and Vanitas with him. In ''Kingdom Hearts III'', Eraqus shows the ability to manifest a temporary physical form, as he is able to interact with Xehanort.

In the original Kingdom Hearts, some disembodied hearts manage to escape the destruction of their worlds, becoming Summon Gems. Through the magic of the Fairy Godmother, Sora is able to use them as summons—temporarily giving them form, so that they may fight by his side. They do this through their own will and are fully conscious of themselves, as revealed when [[Simba]] and [[Mushu]] remember their adventures with Sora in ''Kingdom Hearts II''. Finally, Ventus's and Terra's Keyblades, presumably directed by their hearts, rescued Aqua at one point in the Realm of Darkness, while Ventus's heart eventually resurfaced inside of Sora's to protect him from being corrupted by a Nightmare [[Dream Eater]].

Newly born hearts have even stranger, more unique abilities. Sora's was able to seek out and unite with the broken fragments of Ventus's simply because Ventus was brought to Sora's homeworld. As a result of this, Vanitas took on an appearance similar to Sora's. The merge stabilized Ventus's heart, allowing him to eventually recover. This also resulted in Sora and Ventus to form a connection, granting Sora the ability to sense Ventus's pain and suffering and, with Riku's guidance, reached out to Ventus's heart and allowed Ventus's heart to stay in his body. This would later cause Sora's Nobody, Roxas, to take on Ventus's appearance when Ventus's heart remained within Sora's body when the latter became a Heartless. Xemnas and [[Xigbar]] also revealed that a new heart could be "nurtured," even to the point where it became an exact replica of another person's heart, although they implied that they needed the power of Kingdom Hearts in order to do so.

Unlike other enemies seen throughout the ''Kingdom Hearts'' series, the [[Unversed]] lack a direct connection to the heart. Instead, they are the embodiment of negative emotions, produced when Ventus's heart was split in half by Master Xehanort to create [[Vanitas]]. It is implied that they feed off of negative emotions let off from the hearts of others, growing stronger, and in turn make Vanitas stronger when they are slain and flow back into him.

To wield a [[Keyblade]], one must have a strong heart, whether it be a heart of darkness or light, and they must have [[Bequeathing|touched a Keyblade before]] or inherited the ability from one who has. Roxas could wield a Keyblade even though he did not remember his time as Sora, but it took an effort to get it to materialize in the beginning, and he was not aware of all of its properties, such as returning to the wielder's hand when called. Xemnas, however, did not wield a Keyblade, which remains a mystery. Nomura has implied that he intentionally wasn't using one, which some have taken to mean that Terra prevented it. Riku implied becoming a Heartless makes one unworthy, telling Ansem that "darkness took [his] heart, and the Keyblade with it".