Keychain

The keychains that are attatched to a keyblade are their for few possible reasons. As of one they carry the consciousness or semi conscioussness and will the keyblade itself holds. Two the keychains can act as talismans, they 'funnel' or release magic through the keyblade. Each keychain resonates its own type of energy or frequency allowing the keyblade depending on the power and frequency of its carrier/ bearer to have a unique appearance and ability.

While King Mickey's Kingdom Key, Riku's Way to the Dawn, and Kairi's Keyblade all have Keychains, Sora's seems to be the only one that can change them. However, this may be because only Sora collects them, and the others feel they are unimportant. It seems that the Keychain is what makes a Keyblade a Keyblade; False Keyblades, such as the Dark Keyblade, lack such a feature.