In Kingdom Hearts 358/2 Days, Ultima Weapon is an ability panel. If the user's equipped weapon has a base Strength of +85 or less, the Strength bonus from Ultima Weapon will raise that to +100. If its base Strength is greater than +85, the bonus will be +15. This applies both to weapons equipped through Gears and to Gear-less weapons.
Learning Ultima Weapon
Kingdom Hearts 358/2 Days