Very first thought that popped into my head since watching the season 9 finale. I just have been really busy with work so I haven't had the chance to write it up until now.
Cas watched as the man he once knew paced around the small room. Sam had called him down after Dean had awoken, and Cas had found him locked in the same room that Crowley had once been locked in. Castiel had turned on Sam, talking to him in a low tone and Sam had explained to him everything that happened while Cas was up in Heaven, destroying the tablet. Dean had indeed been killed, Metatron hadn't been lying about that. The fact that Dean was up and walking was the reason Sam had called him here. Sam hadn't made any deal, he hadn't had the chance. The mark of Cain had brought Dean back...but he was different. Sam had caught the hints, the flick of black when Dean's temper rouse. The tattoo had been removed with a slice of a blade, and Dean's personality had shifted much to how Sam was when he didn't have his soul.
Dean watched Cas from the chair he sat in, chains cuffed to his wrists and ankles. Cas paced closer to him, watching him warily and Dean smirked slightly. It wasn't Dean, Cas had to remind himself of that, no matter what he looked like. Dean had died, the mark had changed him into this...a demon.
"Don't worry, I don't bite...hard...Come on you glare any harder and I might actually combust." Dean chuckles, tugging lightly at the chains and Cas stands right in front of him, pulling his angel blade out slowly. Dean arches a brow. "That won't work. Sam has already tried, every way in the book. I can't die. I'm a special kind of monster. Not a bad one so you can relax I am still a hunter. I hunt the bad monsters, I don't see why I have to be tied up. Not that I really mind, but I prefer being tied up by someone with better interests in mind." Cas grips the blade hard, his body shaking lightly and he gives a low growl.
"You are not Dean, demons don't become hunters."
"This one does because I was Dean, I am the new improved version of Dean. I'm better at hunting than he was in every way. I better at most things than he was." Cas shoves the tip of the blade up against his neck, one hand gripping on Dean shoulder so he can't move. Dean gives a low chuckle, moving to push more into the knife.
"You are not better." Castiel hissed, his rage making him blind and he didn't see how close Dean was until Dean had grabbed his arm and knocked the blade of his hand, before gripping the angel's collar pulling him into a deep kiss. Cas tried to pull back surprised, but Dean had the upper hand, growling and deepening the kiss, biting at Cas' bottom lip before letting go. Cas held back a whimper, placing his fingers up to his lip. It hadn't really hurt, it was more of surprise...surprise that he had liked it. He glared at Dean who was licking his own lips with a wicked grin.
"You seemed to enjoy that. Or am I wrong? Did Dean never give you any of that...oh wait Dean was the kind that lied about his feelings, never told the truth and he certainly never would have kissed you. See I'm already better. Now if you want some real fun, undo the cuffs we can go up to the bedroom and I can give you what he never would have. Unless you don't have feelings for him but I don't know you sure as hell act like you do." He holds out his wrists, jangling the chains. Cas swallowed thickly before moving and snapping his fingers the cuffs coming off. He wasn't completely sure this was a good idea, but he wanted it to still be Dean. Even if he was different, and this was what Dean had always hidden from him. Dean rubbed his wrists, getting his feet. Cas flinched at the hand placed on his shoulder, Dean's fingers trailing down the angel's arm, gently taking his hand.
"Come on, before Sam figures anything out." He intertwines his fingers with Cas' leading him toward the bedroom, sliding in and closing the door behind them. Cas jumped when Dean removed his trenchcoat, reaching to unbutton his shirt. "Relax, I'm not going to hurt you in any way you wouldn't enjoy." Rips the shirt, tossing it to the ground, turning Cas to face him, kissing him roughly. Cas slid his fingers under Dean shirt, leaning into the kiss, giving a tentative nip at his lip. Dean growled, akin to a purr, tugging him towards the bed, fighting to get both of their clothes off. Tugs Cas' clothes off, pushing him down on the bed. Cas watched Dean remove his own, eyes looking him up and down.
"Do you like what you see angel?" He moves to lean on the bed, sliding in between Cas' legs, wrapping his legs around his waist, rocking slowly against him. Cas gives a low whimper mixed in with a moan. His legs tighten around Dean waist, fingers gripping his shoulders.
"I won't break...Dean please." He gives a surprised look down at Cas before, pushing roughly into him, biting along his shoulder as he picked up a steady pace. Castiel cried out, dragging his nails along Dean's shoulders. Dean trails kisses along his neck and jaw, moving to bite at the angels bottom lip. He revealed in the whimpers and moans that poured from Cas' lip...his Cas. He didn't care if he had to work back into the angel's good graces, whatever left over emotions Dean had hidden deep down, he was feeling them full blown. Cas was his, he wasn't going to lose something so perfect and wonderful. He wasn't going to make those same mistakes that his past self had made. Their moans mixed together, along with the sound of flesh pounding together. Cas whimpered as his orgasm built, heat pulling in his stomach. Dean felt his own fast approaching, his eyes flicking black as he sped up the pace, stroking Cas in time with his thrusts. He could feel the blood pouring lightly down his back from the nail marks and it drove him on.
Dean came with a growl of Cas' name, thrusting in hard, burying his face in Cas' shoulder. The angel screamed out as he reached his own, the room filling with a bright white light. The slam of Cas' wings into the wall, mixed in with his heavy breathing. Dean kissed along his jaw softly, slowly moving to pull out and lay out beside him. Cas whined and cuddled into him purring. Dean shivered at the brush of a wing against his arm, his eyes slowly returning to their normal self. Cas nuzzled Dean's chest softly as his breathing returned to normal and Dean kissed the top of his head softly.
"We are going to have to deal with Sam."
"I can't trust you...you are a demon." Cas muttered softly and Dean shook his head. "I'm not like the others, I'm like Cain. I feel love, I want to do what is right, which is being your hunter. Heaven isn't always right Castiel."
"I have seen more proof of that in my time with you Winchesters." Cas mumbled as his heavy eyes fell closed. He didn't have to think about this now, there would be the morning and then he could consider what choices he would make. Heaven or Dean...his choice was always going to be Dean.
Not sure whether I want to continue this or not and make it until a multi-chapter. Let me know if you guys want it to be. Probably won't continue writing it until season 10 starts, as I have a lot of other things to start and finish.