Keyblade

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.

Development
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 Xehanort 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.

Powers
The Keyblade's main ability is the power to open or close any lock, whether it be a physical object, or even the heart of a person or world. Their ability to unlock a person's heart makes them particularly effective weapons against Heartless and Nobodies, but also draws these beasts to the wielders. Meanwhile, their power over a world's heart allows a wielder to open or seal the barriers between worlds, or even lock the world's heart to protect it from darkness. Keyblades usually exercise this power by emitting a bright, thin beam of light, but can also work by being directly impaled into a person's chest.

In combat, Keyblades are used in a manner similar to swords. Despite most Keyblade's lack of a cutting edge, or the apparent frailty of their design, Keyblades are able to serve as both excellent blunt weapons, and supernaturally precise cutting tools. Keyblades can be used to channel the powers of light or darkness, and are also natural conduits for magic; even Keyblade wielders without formal training are able to perform magic with power rivaling that of expert mages.

Keyblade wielders are also able to modify the size and shape of their Keyblade. This can be used to merely augment their use as weapons, or even to transform the Keyblade into a vehicle called a "Keyblade Glider", which the wielder may use to traverse the Lanes Between. A Keyblade wielder can also attach a Keychain or Gear to their Keyblade in order to transform it into a set size and shape, as well as to channel the Keychain's innate strengths 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.