The Keyblade is a mysterious weapon heavily featured in the Kingdom Hearts series. Sora, King Mickey, and many other characters who are Keyblade Wielders or Keyblade Masters throughout the series have wielded the keyblade, and it is an important element to the battle between the Darkness and Light.
The Keyblade is usually used in fighting, but it has many other abilities. The most important ability featured throughout the series is the ability to lock and unlock any keyhole. The most apparent use of this ability is in the opening and sealing of the keyholes to the hearts of the worlds, as well as opening paths to other worlds. It also can transform into Keyblade Gliders, and, of course, be used to defeat the enemies the present themselves throughout the series. Different keychains can be attached to the Keyblade to change its appearance and form.
The χ-blade (pronounced "chi-blade" because it's the Greek letter "chi" and not an "ecs") is the predecessor of all Keyblades, created to protect and access Kingdom Hearts. Its origins were introduced in Kingdom Hearts: Birth by Sleep, where many sought after the power of Kingdom Hearts and thus created Keyblades modeled after χ-blade, resulting in the Keyblade War taking place and the destruction of the original χ-blade. However, it was split into seven fragments of pure light, which eventually become the seven Princesses of Heart, and thirteen shards of darkness. According to Xehanort, the χ-blade can also be recreated using a heart of pure light and a heart of pure darkness; however, this method is not reliable.
Sora received the Keyblade during the Heartless invasion of Destiny Islands. At about the same time, King Mickey assigns Donald and Goofy to find "the key" and follow it. In Traverse Town, Donald and Goofy identify Sora as the key wielder because of his Keyblade. Sora travels with Donald and Goofy to many worlds, finding and sealing the keyholes of the worlds to protect them from the Heartless. When the trio makes it to Hollow Bastion, Riku reveals that he was meant to wield the Keyblade instead of Sora, and takes the Keyblade for himself, leaving Sora alone. However, soon after, Sora takes the Keyblade back, proving that his own heart was stronger than Riku's. Frustrated and confused, Riku acquires a Keyblade from Ansem, one that he uses to unleash the darkness from people's hearts. Riku, now possessed by Ansem, later confronts Sora and attacks Sora to free Kairi's heart, needed for both the Final Keyhole to Kingdom Hearts and his own Keyblade. Sora defeats the Ansem-possessed Riku and uses the Keyblade of heart on himself to release Kairi's heart from within. At the End of the World, the trio attempts to close Kingdom Hearts after defeating Ansem. Riku and King Mickey then appear, and the King reveals that he had been traveling through the Realm of Darkness in search of the Realm's Keyblade, the Kingdom Key D. They closed the door and, together, Sora and Mickey seal the Door to Kingdom Hearts.
The second game continues Sora, Donald, and Goofy's journey in search of Riku and King Mickey. Along the way, they come across and confront the mysterious Organization XIII. They learn from Axel during the Heartless invasion that the Organization was using Sora to create Kingdom Hearts because every Heartless slew with the Keyblade was releasing a heart that found its way to Kingdom Hearts. In this dark moment, Sora finds himself conflicted over continuing to defeat the Heartless and releasing hearts or stop the Organization's plot of using the release hearts by defeating Heartless and allow the Heartless to roam free. Goofy assures him, however, that it was far more important to defeat the Heartless threatening the worlds than to foil that part of the Organization's plans. Later, in The World That Never Was, Riku gives Kairi a Keyblade of her own. Riku's own Keyblade had changed appearance to confirm his decision to walk "the road to dawn."
Because of Roxas' ability to wield the Keyblade, Organization XIII uses Roxas to slay Heartless with the Keyblade and create a replication from him, Xion, who was also able to wield the Keyblade. After Roxas defeats Xion, he reclaims his Keyblade from her and eventually unlocks the ability to dual-wield the Oathkeeper and Oblivion Keyblades.
The prequel game introduces the levels of the Keyblade through a concept of the Mark of Mastery exam, which Keyblade wielders must pass in order to be considered true Keyblade Masters. In addition, the concept of Keyblade Armor and the ability to convert the Keyblade into a Keyblade Glider is introduced. Xehanort also reveals the origins of the Keyblade and the original χ-blade during the Keyblade War. In his own pursuits to recreate the Keyblade War, Master Xehanort attempts to pit Ventus against the embodiment of his own darkness, Vanitas. Though he fails, he leaves open many means for him to continue to pursue his goals.
Sora and Riku go through the Mark of Mastery exam to become Keyblade Masters. Towards the end, Master Xehanort returns and reveals his new plan to recreate the Keyblade War. He reveals that at the end of the Keyblade War, the χ-blade was destroyed into twenty pieces, seven of light and thirteen of darkness. Knowing this, Xehanort reveals his plan to pit thirteen beings of darkness against seven of light. This was the purpose of the original Organization XIII, but since it failed, the new plan consisted of a new Organization made up of thirteen Xehanorts. Riku, Mickey, and others are able to foil Xehanort's plan, which included Sora as the last vessel, by saving Sora. Master Yen Sid, however, reveals that Xehanort will still go through with his plan because if they do not come up with seven guardians of light, Xehanort will target the Seven Princesses of Light. Either way, the χ-blade could be forged and a new Keyblade War created. Lea, Axel's original persona, is revealed to have asked for the ability to wield the Keyblade, which he is able to at the end of the game.
Sora, Donald, and Goofy search for a new Keyblade, the Keyblade to Return Hearts. The game also features Xehanort's new Organization and his attempt to forge the χ-blade in his pursuit to recreate and restart the Keyblade War.
When the final confrontation occurs in the Keyblade Graveyard, Master Xehanort is able to successfully reforge the χ-blade after forcing Sora, Riku, and King Mickey into attacking him by striking down Kairi in cold blood. However, during the final battle in the world within Kingdom Hearts, Master Xehanort is defeated, and after accepting defeat and realizing how far he had fallen in trying to make his ideals a reality, he turns the χ-blade over to Sora, entrusting him with it from that point onward.
The Keyblade is the Ultimate Unlock in Disney INFINITY: 3.0 Edition. It is obtained by collecting every available 3.0 figure so far released as of March 15, 2016. This does not include Baloo or Black-Suit Spider-Man, as they are released in different dates.