Omega Weapon

The Omega Weapon (オメガウェポン) is a form of the Kingdom Key that is changed into the Omega Weapon with the Pandora Gear equipped.

Trivia
Its name is originally from the recurring superboss in the Final Fantasy series, usually connected to Ultima Weapon, another powerful superboss in the Final Fantasy Series, reflecting on Roxas's Connection to Sora, who can wield the Ultima Weapon.