Ultimate Form is a Form in Kingdom Hearts III. It is triggered exclusively by Ultima Weapon and changes Sora's clothes to a design very similar to Final Form. It allows him to teleport around the battlefield and use multiple swords to overwhelm enemies with fast and powerful swipes that also possess great range.
Ultimate Form is signified by Sora's clothes adorning a silvery-white and black color scheme, similar to Final Form. Black wisplike stripes can be seen on his pant legs and three crowns on each of his sleeves. While wearing his original outfit during the Olympus episode, Sora's clothes do not change.
In this Form, Sora wields a myriad of swords. His main sword is the Formchanged Ultima Weapon itself, which is rainbow-colored with a red heart symbol near the guard. Its blade is split into two segments and is pointed towards the tip. The auxiliary swords all have various designs and colors, but appear similar with gilded and ornate designs and guards.
Ultimate Form is the strongest Formchange in terms of raw damage, especially given that the Ultima Weapon comes equipped with Combo Boost and Air Combo Boost. The fast and multi-hitting nature of Ultimate Form's blades also complements Ultima Weapon's situation boost, giving it a supportive function in building situation commands for other Formchanges and grand magic. The attacks themselves have excellent range and have great cancel windows for blocking or dodging incoming attacks. Ultimate Finish is especially devastating, hitting multiple enemies around Sora before unleashing large swords of light that circle around him similar to Salvation. Sora can teleport towards his targets by pressing the attack button if he is within range and his dodge will be affected based on whether or not Aerial Dodge is equipped. If equipped, Sora will perform a teleport dodge that covers a similar distance but has greater invulnerability and reaction. Should Aerial Dodge be unequipped, Sora will perform an Air Slide that covers more distance.
Ultimate Form's attacks are hard hitting and do more damage as the length goes on, but it is important for Sora to keep in mind the nature of the attacks themselves. When Sora spins his swords against an enemy, he will send them flying into the air. Sora can choose to continue his combo from there with spiral droves or switch to another Keyblade mid combo. Following up with spiral droves allows Sora to bring down aerial enemies. If too high in the air, the enemy will fall down too far for Sora to follow up with his other combo finishers. At that point, Sora should follow up with an attack that brings him down to the enemy's position such as the hyper/boom hammer's downward slam or falling slash. The attacks themselves do physical damage only, so equipping magic boosting accessories will not make a difference outside of making infinity circle stronger.
Blade Barrier has the same benefits as a normal barrier while in Guardian Form, allowing Sora to block attacks from all angles and cannot be guard broken. Second chance and withstand combo are inherent passives when in Ultimate Form and can save Sora if he has not obtained them through leveling up and he cannot be stunned while in it.
Ultimate Form has no real major downside and is excellent for any combat scenario. Whether it is for fighting bosses or mob fights, Sora is a force to be reckoned with thanks to his enhanced attack power, magic, high mobility, and defensive capabilities.