| Ultima Weapon | |
 "The Key of the Gods. Represents the ultimate balance." | |
| Strength | Magic |
| +7 | +7 |
| Defense | Speed |
| +7 | +5 |
| Wielder | |
| Kleatus Synestyr | |
| Ability | |
| Full Deck | |
| Obtained | |
| Fusion of Retribute and Saving Jane | |
The Ultima Weapon is the ultimate Keyblade available to the player in ''Kingdom Hearts: Sinister'', and is only available after the first completion of the game. It requires a fusion of the Retribute and Saving Jane Keychains (which represent Kleatus' and Abyline's Keyblades, respectively), which can only be done by purchasing the "Original Sin" item at the Moogle Shop, which allows the Retribute to be obtained once again, even through the Ultimate Order Keychain is still in stock. Its ability, Full Deck, gives the player an unprecedented 13 Command Slots - more than twice the original amount! Because of this, the Ultima Weapon is a necessity when facing the Xembur secret boss, because it allows you multi-stock healing and status recovery commands, as well as allowing a myriad of attacks to be stocked.