Keyblades

Keyblades (キーブレード, Kīburēdo) are mysterious weapons that are prominently featured in the Kingdom Keymasters series. These weapons play an important role in the battle between Darkness and Light; they are wielded by many of the series' major characters, particularly one of its main protagonist, Sora.

"This is what lights the darkness. A chance to make everyone happy!"
 * —Sora to CLU, referring to the Keyblade.

Appearance
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, with the exception of the Fenrir, which is instead modeled after a pin tumbler lock key.

Powers
"The Keyblade. A truly marvelous weapon... were it only in more capable hands."
 * —Xemnas during Sora's first visit to Hollow Bastion.

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. For objects like treasure chests, this merely requires tapping the chest, while for more magical locks, the Keyblade generally operates by emitting a bright, thin beam of light from its tip, or by being thrust directly into the keyhole or person'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.

Creation
The original χ-blade's existence was intimately linked with the existence of the true Kingdom Hearts, and so it was destroyed along with Kingdom Hearts in the first Keyblade War. Though Master Xehanort's research suggested that it can be reforged by fusing a heart of pure light with one of pure darkness, he later concludes that the χ-blade can be truly restored only by uniting seven hearts of pure light with thirteen hearts of pure darkness. 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 Ganondorf.

Early history
Long before the events, in the "age of fairy tales" when the world was whole, Kingdom of 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 the Kingdom of Hearts, people 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 who served the light, those who served the darkness, those who sought balance, and those who simply sought power. The conflict embroiled even those who did not desire Kingdom of Hearts and took the lives of thousands; it also extinguished the light from the world and trapped the Kingdom of Hearts in the deepest darkness. The final site of the Keyblade War had soon became the barren Keyblade Graveyard, littered with ancient Keyblades.

Because light remained in the hearts of children, it was able to draw the fragments of the World back together, creating several 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 a weapon meant to bring salvation or destruction.

Before Birth by Sleep
Long before Sora's journey, Xehanort and Eraqus became apprentices under an unnamed Keyblade Master, and they served to protect the Realm of Light from darkness. However, Xehanort's natural curiosity about the darkness and his research into the Keyblade War eventually led him to believe that the sovereignty of light upheld by the Keyblade wielders was tyrannical and misguided. Xehanort sought to create a world in which light and darkness existed in equilibrium; due to the lack of balance between these two forces, if he was to accomplish this goal, he would need to unleash a flood of darkness upon the worlds in the form of a second Keyblade War.

While both Xehanort and Eraqus were declared Keyblade Masters, their differing opinions regarding the start of a second Keyblade War caused Xehanort to leave the Land of Departure. Eraqus became the Successor, and he took on Terra and Aqua as his apprentices. Elsewhere, Xehanort resolved to recreate the χ-blade, and when his pupil, Ventus, refused to submit to the darkness, the elderly Keyblade Master extracted the darkness in the boy's heart to create Vanitas. This left Ventus's heart incomplete and almost resulted in the boy's death, but when he survived, he was left in Eraqus's care. In time, Vanitas would be forced to clash with Ventus, thus forging the χ-blade.

Meanwhile, a semi-retired Keyblade Master named Jolnir took on Arthoross as his apprentice. A former colleague of Eraqus and Xehanort, Jolnir decided not to involve himself in their quarrel over the start of another Keyblade War. Instead, he chose to keep watch over the balance between light and darkness and oversee Arthoross' Mark of Mastery exam.