The Keyblades (キーブレード Kīburēdo ) are mysterious weapons that are heavily featured in the Kingdom Hearts series. Wielded by the main character, Sora, as well as a number of other important characters, the Keyblade is a main part of the battle between Darkness and Light.
According to an interview with Tetsuya Nomura, the original weapon shown during development was actually a chainsaw-like weapon. This was eventually scrapped in favor of the Keyblade.
 Early history
Long before the events of the Dark Seeker Saga, in the "age of fairy tales" when the World was whole, Kingdom Hearts gave light to the world. However, it remained out of mankind's reach, as it was protected by its counterpart, the χ-blade. Eventually, many came to desire the light, and their greed and jealousy introduced darkness into the World. In order to conquer the light of Kingdom Hearts, they forged the first Keyblades in the image of the χ-blade, and they clashed with each other in a great Keyblade War that involved those that served light, those that served darkness, those that sought balance, and those who simply sought power. The conflict embroiled even those who did not desire Kingdom Hearts and took the lives of thousands, as well as extinguishing light from the world and trapping Kingdom Hearts in the deepest darkness. The final site of the Keyblade War became the barren Keyblade Graveyard, littered with ancient Keyblades.
However, because light remained in the hearts of children, it was able to draw the fragments of the world back together into separate worlds. The remaining Keyblade wielders decided to use the Keyblade in order to protect what was left of the Realm of Light. They primarily settled in worlds within the Realm Between, such as the Land of Departure, where the Realm of Light bordered the Realm of Darkness. Memories of the Keyblade War survived in various legends, which disputed whether the Keyblade was used to save the world or to wreak chaos and destruction upon it.
 Before Kingdom Hearts Birth by Sleep
Long before Sora's own journey, Xehanort and Eraqus became apprentices under an unnamed Keyblade Master, serving to protect the Realm of Light from darkness. However, Xehanort's natural curiosity about the darkness and research into the Keyblade War eventually led him to believe that the sovereignty of Light upheld by the Keyblade wielders was tyrannical and misguided, and that a balance of both light and darkness was necessary; due to the extreme imbalance, this would require him to unleash a flood of darkness upon the realm in the form of a second Keyblade War.
While both Xehanort and Eraqus were eventually declared Keyblade Masters, their disagreement over whether the Keyblade War should be reenacted led Xehanort to leave, while Eraqus remained and became the Successor, taking on Terra and Aqua as his own students; a fellow Keyblade Master, Yen Sid, was aware of their rift but remained out of their affairs. Meanwhile, Xehanort resolved to recreate the χ-blade, using his own pupil Ventus, but when he was unable to convince the boy to submit to darkness, he ended up taking what darkness there was in the boy's heart to create Vanitas as a component for the χ-blade, and when Ventus's incomplete heart of light proved able to survive, he left the boy with Eraqus to one day use him as the other half of the artifact.
 Kingdom Hearts Birth by Sleep
Ten years before Sora's first journey, there were eight known Keyblade wielders: Eraqus and his three pupils, Ventus, Aqua, and Terra, Master Xehanort, Vanitas, the retired Keyblade Master Yen Sid, and his apprentice, Mickey Mouse.
When he visits the Destiny Islands, Terra performs the Keyblade Inheritance Ceremony with Riku, making the child into a potential Keyblade wielder, and Aqua accidentally does the same with Kairi in Radiant Garden. She initially intends to perform it with Sora, but she decides against it when she sees that Riku has the ability already. However, Sora unwittingly gains the potential to wield a Keyblade himself when Ventus joins his heart with Sora's after Vanitas's defeat and the destruction of the χ-blade.
When they confront him at the Keyblade Graveyard, Master Xehanort explains to Terra, Aqua, and Ventus that the Keyblades at the Keyblade Graveyard are the remains of the Keyblade wielders after the Keyblade War.
 Kingdom Hearts
When the worlds first started to disappear, King Mickey realized that Kingdom Hearts was going to be opened, and went to the Realm of Darkness to find its Keyblade, with which he could seal the door. However, he would also need someone to use a Keyblade from the Realm of Light in concert with him, so he left a letter for Donald Duck and Goofy, asking them to find the chosen wielder of that Keyblade and assist him in saving the worlds.
When the Heartless invade Destiny Islands, Sora rushes to the small island to save his friends, but finds that Kairi and Riku have already been swallowed by darkness. It is at this point that the Keyblade which Terra had promised Riku finally appears on the island, but because Riku has already given himself to darkness, Sora becomes its wielder instead. When Sora first arrives at the Traverse Town, he meets Leon, who gives him shelter and some insight about the Keyblade and Heartless. Yuffie and Leon have to get Sora off the Keyblade since it's the only way to "conceal his heart (Sora's)," this is due to the Heartless fearing the Keyblade and they will stop at nothing to eliminate the wielder of the weapon.
On Atlantica, King Triton is enraged when he finds out that Sora is the key bearer and he tells him that as a key bearer, one must not meddle in the affairs of another world and that Sora had violated the principle. He declares that the Keyblade and its wielder can only shatter peace and bring ruin.
Sora uses this Keyblade to seal the Keyholes of the worlds he visits, but when he arrives at Hollow Bastion, Riku reveals that the Keyblade was intended for him, and he takes it back as Sora's heart falters. However, Sora soon confronts Riku again, and the strength of his heart proves greater than Riku's, allowing him to reclaim the Keyblade.
Confused and angry, Riku runs off and is found by Ansem, who convinces Riku to allow Ansem to possess his body in exchange for more power. While possessing Riku, Ansem summons the Keyblade of heart, created from the collected hearts of the Princesses of Heart, in order to unlock the Final Keyhole. However, both the Keyblade and the Keyhole remain incomplete due to the disappearance of Kairi's heart. When Sora tracks down the possessed Riku and confronts him, Ansem reveals that Kairi's heart is in fact within Sora, and he attacks Sora in order to take it. Sora defeats him, but in order to restore Kairi's heart and fully seal the Final Keyhole, he uses the Keyblade of heart on himself. This completes the Keyhole and restores all of the Princess's hearts, but Sora becomes a Heartless, until he is restored to his body by Kairi's light.
Later on, after Sora, Donald, and Goofy defeat Ansem and attempt to close the door to Kingdom Hearts, King Mickey finally appears with the Kingdom Key D, a Keyblade of the Realm of Darkness. With their help, as well as that of the restored Riku, they close the door, saving the worlds from the imminent flood of darkness.
 Kingdom Hearts: Chain of Memories
Since Sora retained his memories and feelings as a Heartless, something only one other person had done, Axel becomes particularly interested in why the Keyblade chose Sora as its wielder. Tired of Xemnas's rule, Marluxia conspires with Larxene to use Naminé to rewrite Sora's memories so they can use his Keyblade's power to overthrow the Organization.
 Kingdom Hearts 358/2 Days
As Sora's Nobody, Roxas can use his Keyblade. In addition, Xion is created by Xemnas to ensure there will be a Keyblade wielder loyal to the Organization. Upon Xion's destruction, Roxas awakens the ability to wield two Keyblades, Sora's and Ventus's. The Keyblade was used during this time as part of Xemnas's plans for his Kingdom Hearts.
 Kingdom Hearts II
Sora, Riku, Kairi, Roxas, and King Mickey can use the Keyblade. Sora uses the Keyblade to open new paths to new worlds through Gates. While King Mickey comes out occasionally to assist Sora, Riku obtains his own Keyblade, Way to the Dawn, at some point before reuniting with Sora and Kairi in The World That Never Was. During the Heartless surge in the Castle That Never Was, Kairi obtains the Destiny's Embrace from Riku.
 Kingdom Hearts coded
Data-Sora can use his digital version of the Kingdom Key to fix the World source of Bug Blox and to seal the data Keyholes. His digital Keyblade was destroyed in Episode 5, but gained a new Keyblade in Episode 6. King Mickey explains that this Keyblade is tightly connected to the Power of the Heart, implying that his Keyblade is genuine.
King Mickey also uses his own Keyblade to defeat the Heartless that attack his castle.
 Kingdom Hearts 3D: Dream Drop Distance
Sora and Riku take the Mark of Mastery Exam to become true Keyblade Masters. After his return, Master Xehanort uses his Keyblade in an attempt to turn Sora into his thirteenth vessel. It is later revealed that Lea has become a Keyblade wielder, as well.
All Keyblades share the same fundamental features, modeled after a key: a guard with a handle, a hilt, and a head at the end of the shaft that resembles the teeth of a skeleton key. The exception is the Fenrir, which is instead modeled after a pin tumbler lock key.
The lesser Keyblade of heart, whose existence opens a path to Kingdom Hearts, can be forged from the union of seven hearts of pure light.
The method for forging a regular Keyblade is not entirely clear, although several newly-forged Keyblades do appear in the series. Riku's Keyblade, the Way to the Dawn, was able to manifest by using his Soul Eater as an intermediary, while Data-Sora's strength of his heart allowed him to create a true Keyblade after his artificial, digital Keyblade was destroyed by Maleficent.
 Keyblade wielders
The Keyblade only lets a chosen wielder hold it, but those with the strength of heart to wield a Keyblade are able to give or take them from others, or take control of them if they have been abandoned. Those incapable of wielding a Keyblade cannot keep it, even if a wielder hands it to them. A wielder is able to summon or dispel their Keyblades at will; however, it is implied that one can only wield a single Keyblade at a time, even if they have possession of more than one. The exceptions to this rule are Sora and Roxas, who can wield two Keyblades at once and channel both their abilities, due to Sora harboring Ventus's heart.
It is also possible for a wielder at the level of a Master to choose someone of a strong enough heart as their successor. This is often done through the Keyblade Inheritance Ceremony, but can also be performed informally when the wielder lets a candidate touch their Keyblade, or if their hearts link together.
When some wielders summon their Keyblades, they are accompanied by visual effects specific to the user.
The Keyblade's signature ability is the power to open or close any lock or door, be it to a physical object, to the heart of a person or world, or to a gate or pathway between worlds. Throughout the series, Keyblades have to used to expose and seal the hearts of worlds, to open both mundane locks and paths to or through the sea between worlds, or to lock, unlock, or extract people's hearts. This is typically achieved through a bright, thin beam of light emitted from the Keyblade, but the Keyblade may also be physically thrust into a keyhole or, in the case of a person's heart, into one's chest.
In combat, Keyblades are wielded in the same way as swords, with the specific style varying with the wielder. Despite many Keyblades' apparent frailty or lack of a cutting edge, Keyblades are able to serve as both excellent blunt weapons and supernaturally precise cutting tools. Keyblades are especially effective against creatures connected to hearts or darkness, including the Heartless, Nobodies, Unversed and Dream Eaters.
Keyblades are natural conduits for magic; even Keyblade wielders without formal training are able to perform magic with power rivaling that of expert mages. Keyblades may also be imbued with magic for a variety of effects, including allowing the wielder to inflict greater damage or deal elemental damage to enemies. Keyblades can also be used to channel the powers of light or darkness.
A trained Keyblade wielder can also transform their Keyblade, changing its size and shape. This can be used to augment its use as a weapon, or to transform the Keyblade into a vehicle form, known as a "Keyblade Glider".
A Keyblade wielder can attach a Keychain or Gear to their Keyblade to transform it into a particular form, affecting both its design and abilities. Equipping a Keychain also changes the effect generated when the Keyblade is summoned; this effect is generally based on the Keychain's symbolism.
 Prominent Keyblade wielders
The most prominent character in the series to use a Keyblade is Sora, who has used them successfully in the two main games in the series (with one minor incident). His ability to use and possess the Keyblade was a major plot point in the first game. He has used more Keyblades than anyone else in the Kingdom Hearts series; the variations are created through various keychains attached to his original blade, the Kingdom Key.
Sora's Keyblade is a "Keyblade of Worlds' Hearts", and nearly all of his Keychain tokens represent some important item from a world he has saved. Usually, Sora is not actually shown to be given the Keychain from one of his many friends, so it is possible that after saving a world, or completing a major step in that direction, the world itself rewards him with the ability to access its power in the form of a unique Keychain.
Keychains that Sora receives from his friends, or from defeating challengers in the Olympus Coliseum, always use a token that is somehow intimately symbolic of that person. While Sora's Keyblade is not specifically a Keyblade of human hearts, like the explicitly named Keyblade of People's Hearts, it is likely that the connections between his heart and those he meets allow him to sometimes access their power as well. Sora and Roxas's Oathkeeper and Oblivion are said to specifically embody Sora's memories of Kairi and Riku and Roxas's oath to Xion before her death (Oathkeeper) as well as her demise (Oblivion) and so it is extremely likely that for "people-Keyblades" like these, the Keychains act as a physical embodiment of the memories Sora and Roxas have of those that are important to them. Keyblades that represent entire worlds likely function the same manner, being formed from Sora's memories of that world.
 King Mickey
The King of Disney Castle, King Mickey's Keyblade is known as "Kingdom Key D". It looks the same as Kingdom Key, but its colors are inverted compared to the Kingdom Key. In Kingdom Hearts coded and Kingdom Hearts Birth by Sleep, he uses the Star Seeker, the Keyblade he used in his days as an apprentice under Yen Sid.
Sora's best friend and rival, he wields the Way to the Dawn Keyblade, though in Kingdom Hearts he briefly took possession of Sora's Kingdom Key. In Kingdom Hearts, he stayed behind with King Mickey in the Realm of Darkness. In Kingdom Hearts: Chain of Memories, he explores the basement of Castle Oblivion and struggles in resisting the darkness in his heart, Ansem, Seeker of Darkness, while in Kingdom Hearts II, he helped Sora defeat Xemnas. In Kingdom Hearts: Chain of Memories and Kingdom Hearts, he used the Soul Eater as his main weapon until it transformed into the Way to the Dawn Keyblade.
Sora's Nobody and the thirteenth member of Organization XIII, Roxas also possesses the ability to wield the Keyblade, an ability which Xemnas uses to his advantage by ordering Roxas to gather countless hearts to complete Kingdom Hearts itself. Upon the absorption by Roxas of his Replica, Xion, Roxas regains the ability to wield the two Keyblades, Oblivion and Oathkeeper, an ability passed onto Sora when Roxas fuses with him. Roxas utilizes Gears, which function more or less exactly the same as Keychains would, and create Keyblades that feature apparent Keychains.
 Terra, Aqua, and Ventus
Three Keyblade wielders before Sora, apprentices under Master Eraqus. Sharing a common foe, Master Xehanort, they each suffer horrific fates due to Xehanort's doing at the end of the game: Terra is possessed by Master Xehanort and becomes Terra-Xehanort; Ventus is rendered comatose after his heart is damaged following a victorious confrontation with his dark side, Vanitas; and Aqua is stranded in the Realm of Darkness. All three currently await for Sora to rescue them from their fates.
 Master Xehanort
Master Xehanort is the primary antagonist of the "Xehanort Saga", but makes his appearance through a variety of incarnations, most of which can wield the Keyblade. He himself is a Keyblade Master who plans to restart the Keyblade War; his hybrid form Terra-Xehanort has the same abilities, but is inflicted with amnesia soon after creation and forgets how to use them until shortly before he splits himself into a Heartless, Ansem, and a Nobody, Xemnas. While Ansem is implied to have required Riku's body to wield the Keyblade of People's Hearts, series-creator Tetsuya Nomura has hinted that Xemnas had the ability but intentionally did not exploit it. Master Xehanort's youthful, time-travelling "Young Xehanort" identity can also wield the Keyblade as well as weapons similar to Ethereal Blades, and No Heart, a data simulation of Xehanort in his Keyblade Armor, wields a data simulation of Master Xehanort's Keyblade.