Sad Things I Send My Wife
Cas dies, but because he has grace instead of a soul, his ghost is different. He's able to be self aware- as far as anyone can tell. He glows a ghastly blue and his eyes are gaping holes. When he opens his mouth to speak, a rarity due to how his voice is now, his mouth is also a gaping black hole with shining white teeth. His wings are there, though they swap between feathers and bones. He mostly floats quietly in a corner, keeping to himself and following the item he's attached to (his trench coat?) though if needed or asked he loves to be helpful. Castiel may have finally found peace (if he hasn't he isn't saying so), but for everyone else the situation is heartbreaking.
I’d love to see Gabriel be brought back and he's told he can be restored to his former brilliance but only if he helps restore Cas. Cas gives no help with this of course, if he even can. And Gabe is still an ArchAngel (or maybe just trickster abilities?) but he can't fly unless emergencies because of how tired it makes him. And most of his angel abilities of snapping things up and healing are gone. He can't be killed, and most injuries heal instantaneously, and he doesn't have to eat/drink, but he needs sleep even if its much less than a human, and he's forced to drive across the country in his quest.
He isn't sure when it stopped being about finishing a job for himself, and when it started being out of pity for his brother.
Gabe wearing The Coat and its not fitted to him and it doesn't suit him in any way, but Cas follows the coat so he has to wear it. Plus, it was his brother's coat, something Cas cared about and saw as such a part of himself that he attached to it. He’s not leaving that shit anywhere.
It gets stolen and he has to go claim it from the cops (or whoever had it) and he puts it on, going from frantic and stabby-ready to calm and sad.
person: Uh, not to be rude or anything. But it doesn't seem like something you'd wear.
Gabe: -pauses- -smiles sadly- -turns around and shows a pic of Cas- It’s not. My baby brother wore this and he looked pretty good in it too! -proud of baby brother- It’s... uh... all i have left of him. -looks to the side of the person- -sees Cas' sad ghost face-