The Ultima Weapon is, as the name would probably suggest, the game's most powerful weapon. As a result, it is the hardest weapon to obtain and understand. It is the the rank 3 weapon of Cloud, although given the nature of a rank 3 weapon any character can obtain it. It is a drop from Ultimate Weapon.
Power: ??? - ???
Limit Break: Omnislash
Special Properties: Base power calculated by current HP, can attack while blocking
The Ultima Weapon has the highest base power and MPP of any given weapon. It also has two special properties and a limit break. Therefore, it is the best melee weapon available. However, when low HP, this weapon does not do very much damage. It is important to maintain a high health percentage to use this weapon effectively.
The Ultima Weapon is the most powerful Final Fantasy Sword which calculates damage based on HP. It is often the penultimate weapon or the "Final Reward" requiring a difficult challenge to be completed to obtain. It originated from FF6 and has been used in many installments since then.