The Kingdom Key+ is a stronger, upgraded version of the original Kingdom Key. It has only been used by Roxas and Xion in 358/2 days. It can be used by equipping the Zero Gear and linking three Ability Panels to it. However, it can only be used by Roxas in singleplayer. If you choose Roxas in Mission Mode, you will play as duel-wield Roxas. (Oathkeeper & Oblivion) Xion only uses The Kingdom Key+ in Mission Mode.