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.
In the original Kingdom Hearts, 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.
Kingdom Hearts II continues Sora, Donald, and Goofy's journey in search of Riku and King Mickey. Along the way, the 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 slayed 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."
Kingdom Hearts: 358/2 Days reveals that the Organization had been using Roxas, Sora's Nobody, for their plans in the same way they later used Sora. They made Roxas slay Heartless with the Keyblade, which he could wield as Sora's Nobody, to release hearts from the Heartless. The Organization also made a replica of Roxas, Xion, using Sora's memories. Because of Xion's unique nature and the fact that Sora also harbored Ventus's heart, Xion too could wield the Keyblade. The Organization used Xion to release hearts even faster. Eventually, however, the Organization pit Roxas against Xion, deciding they truly only needed one of the two.
Kingdom Hearts: Birth By Sleep introduces the 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 how they were forged in the image of 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.
In Kingdom Hearts 3D: Dream Drop Distance, 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. T
his 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 vess
el, 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.
Kingdom Hearts III will feature Sora, Donald and Goofy in their search for a new Keyblade, the Keyblade to Return Hearts. It will also feature Xehanort's new Organization and his attempt to forge the Keyblade in his pursuit to recreate the Keyblade War.