[Riku turns back to Terra, shrugging while Highwind pushes off his shoulder again, then flutters over to the other. Friend? :D]

I think you wouldn't have… the way Master Yen Sid explained it, the Realm of Sleep exists as a result of us closing the Door to Darkness. While most Worlds were restored back into being then, some remained asleep in that realm. Waking them was the task for our Mark of Mastery Exam.

As for Dream Eaters… that's how the Darkness takes shape in that Realm… as a Nightmare that feeds of good dreams or as a Spirit that consumes bad dreams.

[Needless to say that Highwind is a Spirit, right? Right.]