Dean never really wonders where all his old clothes go. If there’s a shirt he can’t find, he just assumes it was torn or bloody or somehow ruined by evil, and that he tossed it at the last motel. He just buys more and goes on with his day.
Cas watches as he gets rid of shirt after shirt, leaving bits of himself behind in every town. The town has no idea how lucky it is, Cas thinks. It gets to hold a part of Dean forever.
That thought is what gives Cas the idea.
Soon, the inside of Cas’ trenchcoat is lined with scraps of plaid and old t-shirts, torn from Dean’s destroyed clothing and haphazardly sewn into the lining.
Dean sees it one day, and after a moment of confusion, decides to grin and slap Cas on the shoulder. “Well, you are a Winchester. You should dress like one.” He stares a few more seconds, green eyes going soft as he smiles wider.
It’s not quite everything Cas wants, but he’ll take it. He likes the thought of being a Winchester, likes the possessiveness in Dean’s eyes even more.
He wraps the coat tighter around himself, imagining that his skin can feel the soft fabric through his suit.