Uriel does not have nightmares.
The reason why is simple enough - many years ago, when it was time for him to possess a host, there were enough of his kind that a little training on what to expect and how to react could be afforded. He had near full control of his host's body the moment he entered it some millenia ago.
Castiel is still learning.
Uriel is fond of Castiel, certainly fonder than he lets on, but the frequent questioning when they are alone gets tiresome. For all his filth and blasphemies, Dean Winchester has some use in this regard; he has taught Castiel how to shave, how to barter with money and eat modern food... he has made inroads into adapting Castiel to life on Earth. But Castiel still has much to experience, much to learn.
And Uriel is angered, frustrated, and concerned by that. Castiel has thrown himself fully into the body; he wears it like a human, not a suit of flesh and blood, because no one could be freed long enough to explain how possession of a vessel worked.
Castiel has nightmares, and that frightens Uriel more than the contents of the dreams.
Because it isn't just the dreaming that concerns Uriel. It is how Castiel relates to humans - near idolises them, seeking God's image in all of them.
Uriel knows better. He knows what humans are capable of - what they demanded when he first took a human host.
Sodom and Gomorrah. No towns or cities since had rivalled them, though not for a lack of trying.
Uriel had assisted in burning them to the ground along with every filthy spectacle of a mud monkey to be found within. "God's creatures." A hive of rapists, molestors, torturers, thieves, blasphemers -
Pestilence-ridden fiends, scarce better than the demons they bred. He hadn't questioned the order to lay them to waste.
.
Castiel believes Dean has potential, and by association, that mankind has potential. He looks to Dean for understanding, for acceptance - even, of late, forgiveness and love.
Uriel knows Dean's designs are still selfish - his brother, his kind. That he lacks the courage to do right for the greater good because he sees only what is around him.
He knows the look growing behind Dean's eyes isn't love. It's lust. Not a desire to give, but to take.
He knows where Castiel's nightmares will take him, and it isn't to Uriel's side for knowledge and guidance. It's to Dean's side for something more human; empathy.
Empathy will lead to comfort.
Comfort will lead away from Uriel and towards the same twisted, selfish, wrong path Anna took.
.
He watches, a week later, as Dean pulls Castiel's hands from his ears and holds them down, says soothing, nonsensical platitudes, frowning when Castiel shakes his head and disappears.
.
He watches, a fortnight later, as Dean pulls Castiel's head into his lap and strokes his hair until he falls into a natural sleep, not the near-hibernation slid into whenever the vessel's maintenance requires rest.
.
He does not watch a month later as Dean pulls Castiel by the hips into his lap for something beyond comfort. He does not need to watch. Castiel broadcasts by accident as Anna did deliberately, and Uriel does not need to watch because, instead, he feels; such is the link between them. Dean Winchester pushing into Castiel, over him, fingers and erection and tongue, hungry and wanting. Castiel's head falling back, groans shivering through his body, orgasm racking it further.
Dean Winchester's gasps, moans, whispers and lies.
All humans lie, but they are most brazen of all through sex. Promises that they lack the courage or ability to keep.
He listens to Dean telling Castiel how beautiful he is, how much he means to him, telling Castiel he needs him. He listens and he rages because Castiel is worth more than one human's words, more than lies and blasphemies fuelled by an act born of lust, not love.
He rages because Castiel will not see this. He's rooted himself too deeply in the vessel, confuses lust with love, orgasm with ecstasy.
Castiel deserves better, and will not see it.