Ultima Weapon

The Ultima Weapon (アルテマウェポン) is a Keychain for Sora's Keyblade which appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, Kingdom Hearts II, and Kingdom Hearts Birth by Sleep. It is the most powerful Keychain, and requires the most effort to obtain in all four games. Unlike other Keychains, there are different forms of this Keyblade even though it appears in multiple games.

Design
The Kingdom Hearts version of the Ultima Weapon is strongly reminiscent of the Dream Sword, but is wrapped in ornate gold filigree in a pattern slightly reminiscent of fish bones. The teeth of the blade are a golden version of the crown charm Sora wears, and the Keychain token, attached to the blade by shimmering thread, is a gilded heart, used throughout the series to refer to a complete being, instead of a Heartless or Nobody. It also bears one heart just above the guard and another just next to the crown making up the teeth of the blade, both of which are present in the Kingdom Hearts II version.

The Kingdom Hearts II version retains most of its Kingdom Hearts version elements, except for the colors (blue, white and gold), the crown-and-heart keychain, and the Dream Sword. It also includes many more crowns into its design, including one at the tip of the blade, near the crown "teeth", two making up the guard, three in the chain, and the aforementioned combination of a crown and the original heart Keychain as the token.

The Kingdom Hearts Birth By Sleep version has elements from both previous Kingdom Hearts games. Its style is similar to the Kingdom Hearts version, but its color scheme is similar to the Kingdom Hearts II version. It also uses stars and the lucky charm design instead of crowns and hearts. It is mostly a pale, almost glowing blue with white and gold. The teeth and Keychain are Aqua's good luck charms.

Kingdom Hearts Birth By Sleep
The Ultima Weapon can be acquired for all three characters by clearing the Arena Level 30 match, the final task to complete in the Mirage Arena.

Recipes
Here is the list of synthesize materials needed to obtain the Ultima Weapon in Kingdom Hearts, Kingdom Hearts Final Mix, and Kingdom Hearts II (Kingdom Hearts II Final Mix uses the same recipe in Kingdom Hearts II):

Kingdom Hearts
Ultima Weapon can be synthesized once the fifth list is unlocked.
 * 5 Lucid Gem
 * 5 Power Gem
 * 5 Thunder Gem
 * 3 Mystery Goo
 * 3 Gale

Kingdom Hearts Final Mix
Ultima Weapon can be synthesized once the sixth list is unlocked.
 * 5 Thunder Gem
 * 5 Mystery Goo
 * 3 Mystery Power
 * 3 Gale
 * 3 Dark Matter

Kingdom Hearts II
The Ultimate Recipe is found in a chest at the Mansion: Basement Corridor. The Ultima Weapon is a rank S synthesis item that provides 119 EXP. An Energy Crystal is required to reduce the Orichalcum+ required for synthesis, as there are only 7 in the game; this means that the Ultima Recipe cannot be synthesized unless the Moogles are at least level 2. As Serenity items are part of the recipe, they cannot be used to upgrade it.
 * 13 Orichalcum+
 * 1 Orichalcum
 * 1 Mythril Crystal
 * 1 Dense Crystal
 * 1 Twilight Crystal
 * 7 Serenity Crystal

Etymology
The Ultima Weapon Keyblade is named after the sword of the same name in the Final Fantasy series. The Ultima Weapon is typically shown within the Final Fantasy series as a long sword, with a glowing blue/white blade and a golden handle. It is usually the strongest weapon for the protagonist in the games it appears in.

Other Appearances
Both versions of Ultima Weapon were released with three other Keyblades in a special Play Arts Figures accessory set, Play Arts Arms.

Trivia

 * Through the use of a cheating device, two palette swaps of the Ultima Weapon can be obtained in Kingdom Hearts II. These are the "Edge of Ultima", a palette swap of the original Ultima Weapon, and the "Detection Saber", a palette swap of the second version. When these keychains are accessed in Sora's Items menu, no picture of the Keyblades are shown—only map icons.
 * There is a discrepancy between the artworks of the Kingdom Hearts version of Ultima Weapon and its in-game appearance, namely that the blade's size in the artwork is somewhat smaller in proportion to the handle than in-game.
 * In Kingdom Hearts it is the strongest Keyblade in terms of strength and MP, but in Kingdom Hearts II it is second in strength to the Fenrir and second in magic to the Fatal Crest. In Kingdom Hearts II Final Mix, it is third in magic to Winner's Proof. However, its MP Hastega ability is much more useful in normal combat than the abilities attached to these other Keyblades.