Is depressed and waiting for the finale – hence this...
Castle storage never seemed to change, the contents of his father's locker gathers dust, sure, and new items get deposited there whenever he comes across something too dangerous to be left out in the world. But it always reminds him of Dad, of having someone on the rung above him to defer to on matters of importance. It's a safety net, a lifeline – like his car, his jacket, his amulet and his music.
So many lifelines have snapped, have gone – but he still has this one.
Of course, Dad's long dead, and the rung over him is now occupied by Bobby, but then there's Cas, and he's not even on the ladder he's so far above, watching out for them, there when they need help.
For now, for now he's up there. But soon? Dean looks down at the dusty concrete under his feet and wonders how far you'd have to go to get to hell. Could you even dig your way there? Or is it some separate place, some nightmare of existence? The hole Sam had leapt into looked pretty real to him.
Pretty deep as well.
Dean finds what he's looking for, the small wooden box containing something so exotic his Dad could only dream of it in legend. But then, Dean is more exotic himself. John had Mary, had his sons. Dean has a child that isn't his, a woman who never wants to see him again, a fake father and an angel who somehow managed to work his way under his skin and through his defences without even trying. Castiel is like a brother to him – but when have any of his relationships with his actual family been that simple?
But Death was right, it really was all about the souls.
One more betrayal, one more hard choice to make, one more thorn in his side that Dean can't bear to remove. Castiel twists in him slyly, like a knife, hurting him in all the ways he shouldn't – the ways no friend or comrade should be able to make him hurt, in places no angel should be able to reach. Dean should not care this much that Castiel has been lying to him. He's numbed to Sam's betrayals, but this is fresh and bleeding, weakening him.
But he has one last favour to do for the pale houseman. One more thing to rip out of himself, and cast, bleeding onto the pyre of 'It will never be enough' but he keeps cutting anyway, sacrificing everything he can of himself, trying to die for them – and never quite managing to do it quickly.
He takes Death's ring from his pocket. Another loan to see the job done. He opens the box.
He joins the four rings together and feels the weight in his hand. The last time he held this, Castiel was dead, there was no hope of survival and Lucifer had Sam well and truly under control.
The last time he held this, the world was ending.
Now it just feels like it is.
He's just a man, one man with a moral compass as skewed as his life. But what Castiel is doing, is wrong.
He's just a man, and Castiel is an angel, but he's beaten angels before.
He holds the key to the cage and wonders if this time, this time, he'll win. If this last pound of flesh will be enough to sate the metaphorical demons of his life – the hardest kind to kill.
Tomorrow he's going to throw Castiel into the cage.
Tomorrow he cuts out his heart and feeds it to the devil.