Keyblade
The keyblades are mysterious weapons that partially have a will of their own.
Acquisition
A Keyblade is said to choose its own master. This may be through love, power, or other unknown virtues.
Powers
A Keyblade can utilize magic abilities, such as Firaga magic. Sora's can lock people's hearts, along with the hearts of worlds. Riku's is able to unlock said things. A Keyblade can teleport itself to its master. It also acts like a homing signal to the Heartless. Another feature is that it can lock or unlock any keyhole, not only Keyholes. It is the only weapon that is capable of truly vanquishing the Heartless and Nobodies; otherwise, the Heartless will continue to exist.
Sora's Keyblade
Sora's Keyblade is of the realm of light and was given to him when his home world, Destiny Islands was destroyed by the darkness. Its default key chain is the Kingdom Key. It is commonly referred to within the game as "the Keyblade." Sora's key can seal Keyholes. It is yet to be revealed if any other Keyblades have this power.
Roxas, Sora's Nobody has two Keyblades; one being the Oblivion, the other being the Oathkeeper.
Mickey’s Keyblade
King Mickey’s Keyblade is of the realm of darkness and has an unknown origin, but is assumed to have been acquired in the realm of darkness. It is shown as an inverted version of the Kingdom Key, sometimes known by fans as "The Reverse Kingdom Key."
Riku's Keyblade
Riku's Keyblade is the Way to Dawn. It seems to be an evolved Soul Eater, but not much is clear about this Keyblade. How Riku received this Keyblade is unknown, as he had the Soul Eater in the Land of Dragons, but he had it while in the form of Xehanort's Heartless in The World that Never Was.
Kairi's Keyblade
Kairi's Keyblade was given to her by Riku in The World That Never Was. It is like Sora's keyblade, but represents the Destiny Islands. Tetsuya Nomura has said the scene in which Riku her Keyblade hints at something.
Dark Keyblade
The "dark" Keyblade was a nameless Keyblade made out six of the hearts of the Princesses of Heart. It had the power to unlock peoples hearts and was used by Riku when he was possessed by Xehanort's Heartless. It disappeared when Sora stabbed himself with it to free Kairi's heart.
