Master Yen Sid puts Sora and Riku through a Mark of Mastery exam in order for them to become full-fledged Keyblade Masters and counter the coming return of Master Xehanort. As part of this trial, the two are sent to several worlds that have been restored from the Heartless' attack following the defeat of Ansem, Seeker of Darkness, but have gone into a state of "deep sleep" that disconnects them from the other worlds. These worlds are plagued by Dream Eaters—creatures born from darkness that seek out the sleeping worlds' Keyholes. Sora and Riku's given task is to reawaken the sleeping worlds by unlocking the seven Keyholes they find there and then return to the Realm of Light, after which they will be deemed Keyblade Masters and acquire the power of waking, the ability to free hearts from sleep. The two travel through the sleeping worlds independently from each other after being separated at the beginning of the exam, and recruit benevolent "Spirit" Dream Eaters to aid them in finding the Keyholes and battling the malevolent "Nightmare" Dream Eaters that try to destroy the worlds.
