At first, Castiel couldn't remember much of what he was there for. Maybe so he was there to help an insomniac, or someone with nightmares.

He didn't expect someone in a coma.

For years, he wandered within the confines of someone's mind. Dean Winchester's mind. He saw and felt every daydream, every thought, every nightmare or sweet dream. Through the jade eyes of Dean Winchester, he saw the world as Dean knew it. Bright, with the only concerns being getting out of class and the latest hot girl.

But if Dean perished, so would he. But Dreamwalkers had strange magic. They could heal their hosts, extend lifetimes, visit their brethren for short periods at a time.

But they couldn't fully separate from their host without dark magic. Those who did made only nightmares.

Lucifer, one of them, was locked in the Cage, in the deepest, darkest part of the collective human mind. Humans never explored, none wanting to go deep into their own nightmares.

Even the most powerful dreamwalkers never ventured there.

Not Gabriel, not Raphael, not Michael.

No one dared.