Χ-blade

The χ-blade is a legendary weapon introduced in Kingdom Hearts Birth by Sleep. It is the original after which all Keyblades are imperfectly modeled from. Rather than being a man-made key to an artificial Kingdom Hearts, like the Keyblade of heart, it coexists with the true Kingdom Hearts itself, a perfect union of all hearts and worlds, and is the only thing that can summon its door. According to legend, the Keyblade War occurred because of the many souls who desired to take the χ-blade and Kingdom Hearts for themselves, and Master Xehanort later enacts his plots with the same goal in mind.

The true χ-blade remains lost until the seven lights of the Princesses of Heart or the New Seven Hearts and the thirteen es are reunited. While there are two versions of the χ-blade forged from the fusion of Ventus-Vanitas and clash of the seven guardians of light and the Real Organization XIII, these ones are mere copies and not the real one.

Early history
Originally, the χ-blade was the counterpart of Kingdom Hearts, for which it acted as protector. The Master of Masters studied the χ-blade and learned to extract Keyblades from people's hearts as a result. In the aftermath of the Keyblade War, a conflict over the Lux of the world, the χ-blade splintered into twenty pieces: seven fragments of pure light, which eventually become the hearts of the Princesses of Heart, and thirteen shards of.

Between Kingdom Hearts χ and Kingdom Hearts Birth by Sleep
The χ-blade and the Keyblade War itself passed into legend in the generations after, with the cause of the war itself being distorted by the legends. People came to believe that Keyblade wielders who sought to take the light of Kingdom Hearts for themselves created "Keyblades" in the image of the χ-blade and clashed against one another in the legendary Keyblade War.

Kingdom Hearts Birth by Sleep
In the early stages of his quest to recreate the χ-blade, Xehanort did not want to go through the trouble of having seven lights and thirteen darknesses clash, and opted to find a more efficient method. He eventually discovered the χ-blade can be created when a heart of pure light and a heart of pure darkness, both of equal strength, clashed together, which he noted on one of his reports.

After seeing that his pupil Ventus would be no use to him as a new vessel, Master Xehanort extracted the darkness from his apprentice's heart, creating Vanitas. Once assured that Ventus would survive, the elderly Keyblade Master planned to create the χ-blade by having Ventus clash with his dark half, once he could match Vanitas in strength.

Xehanort set his plans in motion, and the an incomplete χ-blade was forged at the Keyblade Graveyard through Ventus-Vanitas's forced union. Although it appeared complete in the real world, it took on a broken and incomplete form in Ventus's Dive to the Heart. Vanitas attempted to complete the fusion within their combined heart, but Ventus sacrificed himself to stop Vanitas. This caused the physical χ-blade to become broken and unstable during Ventus-Vanitas's simultaneous fight with Aqua and Mickey Mouse, exploding after Aqua clashed against it. The explosion was large enough to blow Mickey, Aqua and the now-comatose Ventus away from the Keyblade Graveyard and into the Lanes Between.

After seeing this failure, Xehanort realized his method of creating the χ-blade was not the correct way to recreate the weapon of legend. As such, he decided to go about it the "proper" way: by finding and uniting the seven pure lights of the Princesses of Heart with thirteen vessels of pure darkness.

Between Kingdom Hearts Birth by Sleep and Kingdom Hearts 3D: Dream Drop Distance
Anticipating failure for his "reckless" attempt to create the χ-blade, Master Xehanort arranges for his ally, Braig, to assist his next incarnation, Terra-Xehanort.

After their experiments plunge Ansem the Wise's other apprentices into darkness and Terra-Xehanort does the same to Braig, he splits himself into the Heartless Ansem and the Nobody Xemnas. Ansem manipulates Maleficent into capturing the seven Princesses of Heart, while Xemnas founds Organization XIII with the intention of using its members as vessels for Xehanort's heart. Master Xehanort's fascination with the χ-blade influences Xemnas to name each of the members of the Organization with an anagram of their original name with the addition of an "X". However, both plans are thwarted by Sora and his friends.

Kingdom Hearts 3D: Dream Drop Distance
Before sending Sora and Riku to undergo the Mark of Mastery exam, Yen Sid reveals the history of the χ-blade while also explaining Xehanort's past.

After his revival, Master Xehanort reveals to King Mickey and Riku that the actions of Ansem and Xemnas were to restore the legendary weapon by having the thirteen darknesses that are the vessels of Xehanort's heart clash with seven lights.

Although Sora had ruined the initial plan, Master Xehanort had anticipated interference and arranged for Ansem to go back in time and share his time-traveling ability with Young Xehanort, sending him to gather twelve incarnations of himself from across time to form a second Organization XIII. After failing to "recruit" Sora as the final Organization member, the gathered members return to their respective places in time, with the intention of meeting again in the future to recreate the χ-blade.

Kingdom Hearts III
Master Xehanort finally forges the χ-blade in the Keyblade Graveyard, after all clashes between the Seven Guardians of Light and his thirteen seekers of darkness have taken place, the final clash being an enraged Sora attacking Xehanort himself after he crystallizes Kairi. Xehanort's No Name turns into the χ-blade, which he uses to open Kingdom Hearts.

After his first defeat within Scala ad Caelum, Xehanort summons the χ-blade, trying to use its power, alongside Kingdom Hearts', to defeat Sora in a final battle. However, Sora manages to defeat the elderly Keyblade Master, who hands the χ-blade over to him after Eraqus's heart, housed within Terra, makes him see the error of his ways. Sora then uses the χ-blade to close Kingdom Hearts for good.

Design
The χ-blade appears to be made up of two crossing Kingdom Keys, with the teeth facing outward. It has a filigree that slightly resembles one on the Ultima Weapon, and the blade slightly resembles the Dream Sword.

The incomplete χ-blade's coloring is more red-orange than bluish-yellow, and the blade is slightly covered with an aura of darkness. It also has chips in the side of the blade, lacks a part of the filigree on one side, and part of the Kingdom Key's hilt is missing, making it look somehow broken or shattered.

The Keychain is a black and red heart that is similar to the Heartless symbol, only without the fleur-de-lis bottom and jagged cross, with two Kingdom Keys crossed over it. The chain starts out as two separate chains that form into one.The Keychain's two crossed Kingdom Keys is reminiscent of the of the "Keys to the Kingdom of Heaven". Although it is not seen in this incarnation, it is especially significant that the Kingdom Key has a silver blade and gold hilt, and the Kingdom Key D has a gold blade and silver hilt, matching the keys on the symbol. When the χ-blade hits a target, the released symbols are gold and dark blue stars, symbolic of light and darkness.

In Kingdom Hearts III, the filigree has a sparkling effect with seemingly flowing energy within it.

Master Xehanort and his data replica can Formchange the χ-blade into several transformations, such as floating cannons, a spinning top, whip, chakram, gauntlet claws, and a double-bladed lance.

While the weapon's name is pronounced "Keyblade", it is considered a completely different weapon from Keyblades commonly carried in the series. The "χ" in the weapon's name, alternately pronounced "key" or "kye", is the letter from the. According to Xehanort, this letter means "death" and is "a letter that spells endings".

Notes and references
Χ-blade Llave Espada χ X-Klinge