Keychain

A Keychain (キーホルダー) is a magical piece of equipment that modifies the appearance and abilities of a Keyblade. In Kingdom Hearts 358/2 Days, the Gear Panel function replaces Keychains. Likewise, the Card system replaces Keychains in Kingdom Hearts: Chain of Memories. Cards, however, do not affect appearance, only ability.

Power
The Keychains have the ability to change a Keyblade's stats, grant it special abilities, and give it a new appearance. While most Keyblades have a basic form, like the Kingdom Key, a Keyblade wielder can upgrade and change the form of the Keyblade with a Keychain. In other words, when Sora or another wielder is equipping a "new" Keyblade, he or she is equipping a different Keychain to the Keyblade, changing its form.

Origin
It has not yet been explained exactly what a Keychain is and why it has the power to transform the Keyblade. A wielder usually receives a Keychain after "completing" the events that transpire within a world, but the Keyblade wielder is not shown receiving the Keychain from anyone, save for when Tifa hands Sora the Fenrir Keychain after defeating Sephiroth, and when Kairi hands Sora her Lucky Charm, which turns out to be the Oathkeeper Keychain. These Keychains are often modeled after elements of the world from which they are received in some way.

Exceptions
Sometimes, a Keyblade does not possess a Keychain. One example of this is the Keyblade of People's Hearts, the Keyblade created by gathering seven hearts of pure light. The Keyblades Ends of the Earth, Wayward Wind and Stormfall did not posses Keychains in the Kingdom Hearts II secret video Birth by Sleep. The broken Keyblades from the Keyblade Graveyard do not possess Keychains either. The actual reason for the lack of a Keychain is unknown.

List of Keychains/Keyblades
Kingdom Hearts Birth By Sleep Kingdom Hearts Kingdom Hearts 358/2 Days Kingdom Hearts II
 * Rainfell
 * Stormfall
 * Earthshaker
 * Ends of the Earth
 * Wayward Wind
 * Master Xehanort's Keyblade
 * Master Eraqus's Keyblade
 * Void Gear
 * X-blade
 * Destiny's Embrace
 * Brightcrest
 * Darkgnaw
 * Chaos Ripper
 * Frolic Flame
 * Lost Memory
 * Treasure Trove
 * Stroke of Midnight
 * Fairy Stars
 * Victory Line
 * Mark of a Hero
 * Hyperdrive
 * Pixie Petal
 * Sweetstack
 * Ultima Weapon
 * No Name
 * Kingdom Key
 * Kingdom Key D
 * Jungle King
 * Three Wishes
 * Wishing Star
 * Crabclaw
 * Pumpkinhead
 * Fairy Harp
 * Metal Chocobo
 * Olympia
 * Keyblade of People's Hearts
 * Oathkeeper
 * Oblivion
 * Lionheart
 * Lady Luck
 * One-Winged Angel
 * Diamond Dust
 * Ultima Weapon
 * Kingdom Key (No Gear)
 * Oathkeeper & Oblivion (Zero Gear)
 * Two Become One (Zero Gear +2 Ability Units)
 * Missing Ache (Skill Gear)
 * Ominous Blight (Techinical Gear)
 * Abaddon Plasma (Duel Gear)
 * Pain of Solitude (Loaded Gear)
 * Sign of Innocence (Chrono Gear)
 * Crown of Guilt (Phantom Gear)
 * Abyssal Tide (Lift Gear)
 * Leviathan (Nimble Gear)
 * True Light's Flight (Wild Gear)
 * Rejection of Fate (Ominous Gear)
 * Midnight Roar (Valor Gear)
 * Glimpse of Darkness (Fearless Gear)
 * Total Eclipse (Prestige Gear)
 * Silent Dirge (Crisis Gear)
 * Lunar Eclipse (Omega Gear)
 * Darker Than Dark (Hazard Gear)
 * Astral Blast (Rage Gear)
 * Maverick Flare (Champion Gear)
 * Twilight Blaze (Ultimate Gear)
 * Omega Weapon (Pandora Gear)
 * Aubade (Mystery Gear)
 * Umbrella (Casual Gear)
 * Kingdom Key D
 * Kingdom Key
 * Way to the Dawn
 * Soul Eater
 * Destiny's Embrace
 * Kingdom Key D
 * Star Seeker
 * Hidden Dragon
 * Rumbling Rose
 * Hero's Crest
 * Monochrome
 * Mysterious Abyss
 * Follow the Wind
 * Wishing Lamp
 * Decisive Pumpkin
 * Circle of Life
 * Sweet Memories
 * Photon Debugger
 * Gull Wing
 * Guardian Soul
 * Sleeping Lion
 * Fenrir
 * Bond of Flame
 * Two Become One
 * Fatal Crest
 * Winner's Proof
 * Ultima Weapon