The Keyblade is a weapon heavily featured in the Kingdom Hearts series. It acts both as a sword to defend against the game series' many enemies (which include "Heartless," "Nobodies," and "Unversed"), and as a key to unlock doors, locks, and even hearts. Keyblades can also seal off or open up pathways between the worlds of the Kingdom Hearts series.
Origin and Powers
The first keyblade was called the χ-blade, and while it is pronounced the same way, it acts as a "perfect union between hearts and worlds," while the subsequent keyblades are just replicas. The Keyblade War existed to fight over this χ-blade and occurred long before the first Kingdom Hearts game.
There have been many keyblade wielders throughout the Kingdom Hearts series, which themselves span over ten entries. Keyblades act as the main weapon of both the Keyblade War and the basic battle between Light and Darkness. "Organization XIII" often acts as the series' antagonists, showing up to thwart the hero as they fight with their keyblade throughout several worlds.
Keyblades choose individuals with "strong hearts" to wield their power, but holding the weapon causes you to become a target for the Heartless, which are creatures that feed on the darkness of peoples' hearts. However, it also allows you to fight them, as normal weaponry is ineffective otherwise.
There have been many spinoff games which nevertheless act as part of the Kingdom Hearts lore. These feature alternate protagonists such as Aqua, Ventus, Roxas, and Terra. However, the main two protagonists of the series are Sora and Riku, who are aided by King Mickey, Donald Duck, Goofy, and Yen Sid.
Sora as a Protagonist
Sora, the protagonist from Kingdom Hearts 1-3, as well as some of the spinoff games, obtains the Keyblade in the first Kingdom Hearts game while living at his home on the Destiny Islands. After an unknown darkness swallows his friends, he summons the Keyblade to fight back and ends up acting as the protagonist for most of the series.
Sora acts as a naive, yet strong comic relief character who later admits that he was only chosen by the Keyblade for his strong bonds to his friends, as his token line states, "My friends are my power!"
Because Keyblades choose their wielders, taking away a Keyblade is very difficult, and the protagonist's villains eventually decide to simply trick Sora into doing their bidding through his naivety, rather than take the Key themselves. However, he briefly loses the Keyblade near the end of the first game when his heart wavers.
While the Kingdom Hearts timeline can be confusing, the idea of the Keyblade is relatively straightforward. It can unlock or close any door (including the locks on worlds themselves), the heart of a person (villains often corrupt hearts, and Keyblades can close off that darkness), or gateways between worlds. And, of course, these weapons also exist to channel the powers between the Light and the Darkness.