When he first saw that coat, it held no meaning for him. Granted it was the reason why Dean would refer to Cas as a holy tax accountant. But that night in the barn, it was just a tan trench coat.
Dean noticed that the trench coat was very Castiel when Jimmy had pulled it on to confront the demons possessing Amelia and holding Claire hostage. In appearance, Jimmy looked like Castiel of course. But he didn’t have the imposing stature that Cas exuded. Dean breathed a little sigh of relief when Jimmy gave Cas permission to possess him once again.
Dean didn’t realize how much that trench coat meant to him, how much it symbolized until it floated towards him in the reservoir. Gathering it up, he wrung it out and folded it before putting it in the trunk of the Impala where it stayed until they had to hide the Impala because of the Leviathans. If Cas found his way back to them, he would need the coat.
Pulling the slightly mildewed coat out of the Impala’s trunk, Dean vowed to himself to take better care of the only tangible memory of Castiel. Angry at having to hide his Impala, upset at Sam’s need to alone, and still mourning the loss of Castiel, Dean took his laundry and the coat to the local laundromat. He furiously scrubbed at the coat, imagining tendrils of inky black Leviathan guts staining it. Satisfied that all remnants of those creatures were gone, he dropped it in the wash.
That night, he folded the coat gently and placed it in the trunk of his current car. From then on, he ensured the coat was transferred between cars. Once he and Sam started working together again, Dean waited for Sam to mention it but he never did.
Dean didn’t let the trench coat leave his possession until the day he sought help from the healer Emmanuel.
Seeing Cas wearing the trench coat over his hospital gown felt wrong but right at the same time. Dean didn’t like to dwell on it.
Thankfully, the trench coat was back to being a part of Castiel while they were in Purgatory. It may have been dirty and bedraggled but it screamed Cas. Not to mention how nicely Cas cleaned up after getting out of Purgatory.
He had grabbed at the trenchcoat in the crypt when Castiel almost beat him to death before taking off with the tablet.
It wasn’t until Cas lost his grace and became human that Dean truly realized what the coat symbolized. It had meant something to him before as evidence that Castiel existed, that Castiel cared. Now, staring at the bedraggled human across from him, freshly pulled from the brink of death thanks to the angel inhabiting Sam, Dean realized the coat had always showcased Cas’ status as an angel. He would swoop in, trench coat settling around him and Dean would know that Cas would help them, that everything would somehow turn out okay.
Dean had sent Cas away, as painful as it was, but a part of him whispered that it was okay because it wasn’t his Cas.
When things were falling apart after Kevin’s death and Gadreel running off in Sam’s body, Dean called Cas. Relief flooded Dean as Cas walked in a suit and a trench coat. It wasn’t the exact same but there was something about it that was familiar and reassuring.
From then on, Castiel and the trench coat were inseparable. Dean had winced when he had to burn Castiel’s body. Part of him screamed to keep the coat, to hang on to it, put it in the Impala and bring it back to his room in the bunker. Shaking his head, he wrapped Castiel’s body gently, coat and all.
The only time in recent memory that Cas hadn’t worn the coat was when he pretended to be a doctor to get close to Donatello. Replacing the trench with a lab coat caused a weird sensation in Dean’s stomach that he refused to think about and buried down deep.
Now, as he saw the back of it walk out of the bunker for possibly the last time, his heart wrenched.
“What have I done?” he softly whispered, pouring himself another tumbler full of liquor.