Kingdom Key

The most prominent and famous Keyblade is the Kingdom Key. It appears in every Kingdom Hearts game to date as the "default Keyblade". The key chain attached (the Mickey Mouse insignia) draws out the Keyblade's true form and power. Sora first obtains the Kingdom Key during the destruction of the Destiny Islands in Kingdom Hearts. King Mickey uses a similar weapon that he obtained when traveling through the Realm of Darkness. It was forged in the Realm of Light opposite to King Mickey's being forged in the Realm of Darkness.

Appearance
The Kingdom Key looks like a classic skeleton key. The blade and teeth are silver, while the guard is gold. The keychain is Mickey Mouse's symbol. The reason for this is unknown. It may be due to the fact that Mickey was originally intended to be the main character.

The teeth of the Kingdom Key form the silhouette of a crown. Interestingly enough, the silhouette formed from the teeth seems to match the crown charm on the necklace that Sora wears in all three games.

Users
Though the Kingdom Key is most usually related to with Sora, several others have used it, or copies of it, as well. Upon arrival to Hollow Bastion in Kingdom Hearts, The Kingdom Key is taken by Riku. This was short-lived, as Sora retrieved the Keyblade before fighting him (The Kingdom Key represented the concept of the Keyblade. When Riku took Sora's Keyblade, it appeared as the Kingdom Key, regardless of the Keychain attached at the time). This was the only case in which someone else held the actual Kingdom Key. Roxas is often seen with the Kingdom Key (when not using Oathkeeper and Oblivion). However, this is merely because he is Sora's Nobody, and that connection allows Roxas to have a Keyblade. Xion has also been seen wielding the Kingdom Key, although, it is believed to be a fake, possibly forged on the chains of Sora's memories. The exact origin of this Kingdom Key is unknown at this time. Mickey also uses a Kingdom Key, although his has inverted colors, the blade being gold and the handle being silver. Mickey's Keyblade comes from the Realm of Darkness while Sora's is from the Realm Of Light. At Sunset Horizons, Terra takes this Keyblade (though this is unknown why because Ven should have chosen the Kingdom Key instead and Terra, the Way of the Dawn, but it could be similar to how Riku was originally the Keyblade master, but then went to Sora).

Trivia

 * No matter what keychain you're using when you defeat the World of Chaos it automatically reverts back to the Kingdom Key during the ending sequences of the game.