It's hiatus, it's Friday, it's Fan Fiction Friday!  This installment comes courtesy of YellowEyedSam.  This fic does come warnings of graphic depictions of violence to main characters, otherwise, enjoy a chilling take on Sam's visions.   

***********************************************************************************************************

The demon fell with a howl, clutching its broken nose. It swore at Dean, promising to break more than his nose in return, though only getting so far as the second word before Dean stuck the demon knife into the rambling demons chest.

Dean said not a word as he pulled the knife out and sheathed it. He glanced behind him, checking if the demon had alerted anyone, before carefully proceeding ahead.

He reached the main room without further instances, and found to his surprise nobody here, not even Castiel. He’d barely taken a step in when he felt a presence behind him.

Before he could register who it was, he was punched in the side of his face, causing him to spin and stumble into nearby chairs. With a groan, Dean quickly got his bearings and brought up his gun, but froze when he saw who he was aiming at.

“Sammy?” Dean gasped, immediately rushing to his feet, the pain forgotten momentarily. "Where have you been? We've been looking for you for weeks!"

“Dean,” His brother greeted with a smile that lacked warmth.  “Long time no see.”

Dean stopped dead in his tracks, a sudden feeling of apprehension freezing him in place. Something felt very wrong. Now that he wasn't blinded with relief, he could see something was off with Sam. The way he stood relaxed and unarmed, the way he looked at Dean without warmth. Without realising, he brought his gun back up, aiming it at Sam. Dean glanced to the gun, suddenly aware of his action, but couldn't pull away. His hunter instincts warred with his brotherly ones. “You..." his eyes narrowed, "You can't be Sam.”

Sam looked at with him with a bemused expression. “Perhaps I hit you too hard.”

Dean swallowed his nerves.  "Who are you?"

"I'm your brother Dean, who else would I be?"

"A demon would be my first guess, considering this place is swarming with them.”

His brother gave an amused chuckle.  "No one's possessing me Dean"

"Then you wouldn't mind if I just rolled off some Latin would you?" 

Without giving “Sam” a chance to respond, Dean started chanting an exorcism, but had barely begun when his words were suddenly echoed by his brother. Once he realised that “Sam” was reciting the words with no ill effect, Dean started to falter from shock, eventually falling silent.  As “Sam” neared the end, he approached Dean, who stood transfixed. Unable to move, as if held in place by an invisible force, Dean could only watch as Sam grabbed his shirt and leaned in close with the last words of the exorcism on his sneering lips.

"... Ergo, omnis legio diabolica, adiuramus te!” Sam grinned the moment he finished, and at the same time his eyes went black as if to further emphasize the mockery. Dean barely had enough time for the shock to sink in before he was throw with incredible force across the room, crashing back first into the telescope with an almighty bang, and then falling to the flood with a thud. 

The first thing Dean became aware of was a powerful throbbing headache, crowding out any coherent thoughts.  He could barely utter a groan as the pain from his back further jumbled his thoughts.  Through hazy vision, he could see someone walking towards him, and something in his gut told him to get away quickly.  As he tried to get up, a searing pain shot across his back, sending him crashing back down with a muffled scream.  The pain kept him pinned and helpless, and all he could do was watch with dread as Sam approached. To his surprise, Sam suddenly stopped and turned away.  Confused, Dean looked past his brother and saw a familiar trench coat come into view.

*************************************************************************************

"Hello Castiel," Sam greeted as he turned to face the angel.

Castiel swallowed nervously as Sam turned to face him. “It pains me to see you like this Sam”

Sam gave him an amused look “Oh? And why is that?”

“You fought your destiny, the evil in your blood, only to fall to it by means out of your control,” Castiel said with genuine heartbreak. “You don’t deserve this fate Sam, not after everything you’ve done.”

“Oh, I disagree,” Sam’s voice sank menacingly low as he made his way to a nearby bookcase before plucking a sword from its stand.  “This is exactly what I deserve."

"Please Sam," Castiel implored, "I know whats its like to be consumed by power. It changes you. This isn't want you want, trust me. Its the demon blood making you think that.”

"Is that so?..." Sam's voice trailed off in disinterest, his attention more focused on the blades' edge which he slowly ran his fingers along.

Castiel looked crestfallen as his words feel on deaf ears. Nothing was getting through to Sam and he was struggling to think of a suitable response.

"Finally done lecturing me Castiel?" Sam asked, interrupting Castiel's thoughts. The younger Winchester stalked towards him with the sword still in hand.

Castiel hesitated, taking a step back with his blade raised to defend “I don’t want to hurt you Sam..”

Sam sneered, his lips and fingers twitching. Castiel felt a shift in the air, and had seconds to react as Sam rushed forward faster than he imagined. A mighty clang reverberated through the room, and both weapons bounced back from the force. Without giving Castiel a moment to breathe, Sam slashed with his sword again with such force and Castiel was forced to parry. Such strength was beyond human limits, and Castiel knew he must be tapping into his powers to boost his strength. He couldn’t afford to prolong this fight with what little grace he had left. He had to think of a solution fast.

“Is this really all you can do?” Sam laughed after leaning in close when both became deadlocked. 

“You’ve become so weak” He pushed even harder, forcing Castiel to stumble back. “You’re no better than a human with a few party tricks!”

Castiel grunted from another swing he miraculously blocked. “That may be true,” he said through gritted teeth, “but I am not weak in spirit. I won’t give up on you Sam!” He yelled as he head butted Sam, catching his friend off guard, and making him stumble back dazed. Without giving him a chance to refocus, Castiel rushed forward and shouldered into Sam, shoving him into a pillar hard enough to make Sam momentarily collapse.

His heart still racing, Castiel tightened his fist, mustering the strength to hit Sam hard enough to knock him out. He’d only just taken a step forward when he felt the sword thunk into his chest.

Initially Castiel thought nothing of it. He was an angel, and a wound like this was just a slight hindrance. Then came a searing pain that swiftly robbed him on his energy, causing him to stumble back, and almost collapse. Confused, Castiel looked down and noticed something glittering on the blade's edge.  But before he could so much as touch it, Sam leapt to his feet and lunged, pushing the blade as deep as it would go, eliciting a cry from Castiel.

"Ground up angel blade" Sam said with a grin as he easily snatched Castiel's angel blade from his weak grip. "Not as lethal as the real thing, but powerful enough to stun.”

Castiel watched with horrifying realisation as Sam raised the angel blade. Sam was going to kill him, and thanks to the contaminated blade, he hadn't the energy to move or even speak. All he could do was watch.

Instead of the cold feel of a blade penetrating his flesh, the sound of a bullet went off. The blade destined for his chest sparked, and a split second later was jerked out of Sam's grip from the impact. 

Looking groggily to the side, Castiel saw Dean, standing shakily whilst holding a gun. A flood of relief hit Castiel. But the moment was short lived. Without Sam to hold him up, Castiel hadn’t the energy to stand and collapsed to the floor.

In the distance he heard Dean's concerned voice, but Castiel was too weak to respond. All his energy went to moving a shaky arm to the wound. If he could just pull the sword, he could at least stand, but found even gripping was now beyond his strength. Castiel could only assume the flecks of angel blade lodged in the wound were steadily draining him of what grace he had left. Whatever was happening with him, he was helpless, and quickly loosing conscious. With what little energy he could muster, Castiel took one last hopeful look at Dean before he allowed himself to be dragged down into unconsciousness.

*************************************************************************************

Sam turned back to Dean with a cruel smile, his mouth twitching with barely contained laughter “Just you and me now Dean.”

Dean’s instinct forced him to tear his eyes away from Castiel’s limp form to the bigger threat in front of him. For a moment he felt numb, but the way Sam looked at him made him feel fear on a whole new level, and it brought a horrifying realisation he had so far tried to deny; that this thing really was his brother. 

How, after all these years, and all the battles fought had it come to this? Sam had won against the darkness inside him. He had conquered demon blood addiction twice, so how on earth did the compassionate brother he knew turn into this ruthless thing he saw before him?

“What happened to you Sam? I don’t even recognise you...” Dean’s voice strained with emotion.

Sam snorted in amusement. “I am who I was meant to be Dean. I stopped resisting, and embraced who I really am.”

A sense of deja vu struck Dean as he recalled similar words, back when he was inflicted with ghost sickness. He had hallucinated Sam who had apparently given in to the darkness inside of him, and boasted about it whilst strangling the life from Dean. 

“Sammy no…” Dean’s heart sunk into a chilling realisation. “You can’t let the demon blood control you. Please..“ he begged,  “fight it.”

Finally, Sam laughed, before tilting his head to look at Dean with perplexed amusement. “Really Dean, you believe I would change my ways just because you asked me to?” He shook his head.  “I have no intention of wasting my life pretending to be someone I’m not.”

“Dammit Sam!” Dean yelled, feeling frustrated and helpless.  “Who you were before WAS the real you! I know you wouldn’t willingly give in to the demon blood, so don’t expect me to believe this was your choice!”

Sam gave Dean an exasperated sigh. "Stubborn as usual”

"You're damn right I am. Wouldn't be a Winchester if I wasn’t." Dean allowed himself a sad smile that barely touched on what he felt inside.  "Which is why I can't give up on you, no matter what happens,” his jaw clenched as did his hands around his gun.

"Go ahead then Dean, try and stop me,” Sam taunted, looking like he was on the verge of laughing.

Dean's finger twitched on the trigger, hesitant. Even if his intent was only to wound, it was still difficult, but he had to do this. He couldn't let Sam walk free. If his brother could so easily come close to killing Castiel, then what of others? He had no idea of Sam's intention, but Dean knew he had to stop him right here.

With one last breath to calm his nerves, he fired, but no sound came bar the trigger.  Dean looked at the gun before glancing to Sam and realised, judging by Sam’s smug expression, the gun didn’t jam on its own.

Suddenly, out of the corner of his eye Dean saw what looked to be a group of demon clouds heading out of the open door way.

"What the hell? What’s going on?" Dean asked in confusion.

"It seems I no longer need to keep you busy,” Sam said sounding relieved.

Dean turned to Sam looking alarmed. "Busy? What’s going on?"

"Dean Dean Dean…" Sam shook his head, looking disappointed. "For someone usually so sharp, you're a little slow on the uptake.”

Dean stood there dumbfounded for a moment as he cycled through his memories until something clicked. The panic was obvious on his face. "You've been stalling.”

Sam's smile widened in reply.

Dean opened his mouth to reply when his air supply was suddenly cut off. Instinctively he dropped his gun and grasped at his throat as he fell to his knees, desperately trying to draw breath.

"No more stalling Dean,” Sam said with that smile still plastered on his face. "You'll find out soon enough…" As Sam turned and headed towards the stair case Dean felt the grip on his wind pipe lessen, just enough for shallow gasps.

“Sam..." Dean wheezed, “please..stop!" But his brother ignored him, neither slowing his pace nor looking back.

With each step Sam took, Dean felt his stomach tighten further with despair. He had tried so goddamn hard to stop this situation from ever happening, to spit in the face of destiny, but it had somehow still happened.

So busy in his own thoughts, it took Dean a few seconds to realise Sam had stopped. He looked up, expecting to see him gone, but his brother was still there, hands on the rail in front of the door whilst looking down at him with a feverish glint in his eyes.

"Don't go…" Dean pleaded, his voice so brittle.

“It’s been a fun ride Dean” Sam said “But this is where I get off.”  He then raised a hand and paused, his index finger and thumb touching. "Goodbye Dean,” then snapped his fingers.

All of a sudden Dean heard a muffled roar coming from somewhere in the bunker that seemed to spread quickly from all directions with alarming speed. Something about that sound was familiar, setting Dean's nerves on edge, but he didn't have to wait long as the source of the roaring was already here. Bright lights flickered from the corridors on each side of the entrance room. Seconds later, flames shot out, splitting, and crawling up the wall like snakes, and devouring the surface as if it was made of paper.

Dean watched, horrified beyond belief as he realised Sam's intention was to burn the bunker and everything in it to ash, including him. Through the curtains of fire, Dean slowly looked up to Sam, who regarded him with a triumphant smile on an unrecognisable face. As Dean realised that was possibly the last image of his brother he'd ever see, Sam turned away and walked through the door. Dean screamed his name one last time before the door slammed shut, leaving him to die in a fiery grave.