Each character has a specific ultimate weapon that can be acquired by using the Celestial Mirror. When the weapon is first found, it is equipped with No AP ability. To remove this ability and empower the weapon to it's full potential, you need to find 2 specific event items for each character. Upon doing so, you must then return to the Macalania Woods and use the Celestial Mirror to power up the weapon at the large spherical crystal high amid the treetops. Below is the description on how to get the weapon.