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, and Kingdom Hearts II. It is the most powerful keychain, and requires the most effort to obtain in all three games. Unlike other keychains which appear multiple times, the Ultima Weapon's appearance differs between games. 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, making it the most efficient weapon in the game.

Appearance
The Kingdom Hearts version of the Ultima Weapon is actually the Dream Sword 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.

The Kingdom Hearts II version has, as the blade, the II (like the one in the title screen) with a small crown - similar to Sora's necklace - near the top, covered in a spine-like pattern that, at the top, resembles a heart. On the bottom of the II - not in the handle - is a small heart, possibly referencing the fact that Sora became a Heartless. On the handle, there are two crowns on the protector. The key's teeth are a goldish heart with a crown at the top. The keychain has three crowns and, as the motif, a heart with a crown on its top (like in the teeth). In short, it retains most of its Kingdom Hearts version elements, except for the colors (blue, white and gold) and the crown-and-heart keychain.

Kingdom Hearts
In order to unlock the Ultima Weapon for synthesis, all other recipes must first be synthesized at least once.
 * 5 Lucid Gems
 * 5 Power Gems
 * 5 Thunder Gems
 * 3 Mystery Goo
 * 3 Gales

Kingdom Hearts: Final Mix

 * 5 Thunder Gems
 * 5 Mystery Goo
 * 3 Mystery Force
 * 3 Gales
 * 3 Dark Matter

Kingdom Hearts II
The Ultima Recipe can be found in the Basement. 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

Background
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.

Trivia

 * Through the use of an Action Replay, two extra versions 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.
 * Unlike the returning Keyblades, Oathkeeper and Oblivion, Ultima Weapon's appearance changes between Kingdom Hearts and Kingdom Hearts II. The reason for its change in appearance is most likely due to the change in synthesis ingredients.
 * 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, if you talk to the Moogles in the Moogle Shop some time before creating the Ultima Weapon, one will urge Sora to bring them more materials, and another with say it's because they are hoping to create the ultimate weapon.