Ultima Cannon (アルテマキャノン Arutema Kyanon?) is a technique exclusive to Terra in Kingdom Hearts Birth by Sleep and Kingdom Hearts Birth by Sleep Final Mix. The attack consists of the user transforming his Keyblade into a large cannon, which launches two large balls of energy at the opponent.
In Kingdom Hearts II Final Mix, the Lingering Will's version only fires one ball of energy, though the blast is larger than the Kingdom Hearts Birth By Sleep version, it homes in on its target. Despite this, the attack doesn't do as much damage, and it can be deflected back at the Lingering Will.
In Kingdom Hearts Birth by Sleep, Ultima Cannon is Terra's ultimate Shotlock that has a maximum level of 6 and max lock of 16. After the first ball of energy is fired, the player can increase the damage of the second ball by pressing when prompted. The better the player times his or her button press, the more powerful the second energy ball is.
Learning Ultima Cannon
Terra-Xehanort is able to utilize a version of this technique from Terra, and uses it during his boss battle. The Lingering Will can also use this technique, due to it having all of Terra's former abilities.