Each member of the Royal Guard possesses their own oken in their bones. Aizen was trying to make his own, which was the whole point of the entire Arrancar Arc
So there could be more than one Oken that could permit access to the Spirit King's palace (the consent of the Royal guard, and the making of a different key)
Each member of the Royal Guard possesses their own oken in their bones. Aizen was trying to make his own, which was the whole point of the entire Arrancar Arc
Each member of the Royal Guard possesses their own oken in their bones. Aizen was trying to make his own, which was the whole point of the entire Arrancar Arc