Blood of an Angel

Summary: Lucifer has unleashed an ancient evil. Will the Winchesters and Castiel be able to stop it? When someone is injured, what level of sacrifice can be made to save him? Set somewhere in Season 5. Slight Destiel. Oneshot.

Disclaimer: I do not own anything about Supernatural.

Dean really thought he had heard it all. "Are you seriously telling me that there is a demon overlord?"

"Yes," Castiel stated, unable to keep the irritation from his voice. Sometimes he did not understand why Dean needed to hear certain pieces of information multiple times. "He is called the Asmodai- Demon King."

"And he was was shut away in Hell but now Daddy Devil set him lose?"

"He would be of great help to Lucifer in this battle. He intends to weaken Heaven's power."

"Wait, you mean this super-demon can actually get the better of your holy asses?" Dean had seen Castiel smite demons left and right. There really wasn't much of a contest between an angel and your run-of-the-mill demon.

Castiel cocked his head to the side. "He is one of the only creatures that can kill angels. He transfers venom through slashes or bites that acts as a poison that slowly infects our Grace. Once infected there is about a ten percent survival rate."

"How was he even a problem? I mean he can kill you guys but it's just one demon against all of Heaven. I feel like I am missing something."

"The Asmodai has the ability to convert lesser demons to his race, much like a werewolf transforms your race," Castiel explained.

"Have you fought him before Castiel?" Throughout the discussion Sam had remained silent but now it was time to form a plan.

"Yes," Castiel said. Sam did not miss the trepidation in his voice.

Dean shot him a surprised look. "I thought you said these things were ancient."

"I have existed ever since the creation of the Heavens and Earth, Dean. I am quite old."

"Well excuse me for forgetting with you looking like a middle-aged tax accountant and all," Dean replied sarcastically.

Sam rolled his eyes at his brother and addressed the angel again. "When did you fight them? How did you beat them?"

"He was the first demon created after Michael shut Lucifer away. I was young…it was my first war. By the time we realized there was an evil presence on Earth he had built himself an army. We fought them for a few years but he just kept creating more warriors. The only way we were able to stop them was by trapping the Asmodai in a cage similar to Lucifer's. Without their leader they reverted to the demon we have now."

"Ok," Sam said pacing around the room, "So we need to get to the Asmodai before he starts converting demons."

"I fear it is probably too late for that but if we move quickly we may be able to fight him while his followers are few in number." Castiel went to their weapons and supplies. "There is one way to kill one of the Asmodai's warriors," he grabbed a knife, turning to the brothers, "You must stab it with a blade soaked in the blood of an angel."

"Ok," Dean said, "Luckily we have one of those. Can we gank Papa Bear that way?"

Castiel gave Dean an exasperated expression. "I do not-"

"How do we kill the Asmodai?" Sam interpreted.

"I believe he can be killed in a similar manner. He may require more than just the blood of an angel," he paused, "When I last fought him he was too well protected by his followers to be singled out and killed. However, I do believe we have a higher probability of killing the Asmodai if we act quickly."

"We better be able to gank him…we can't send him back in his box with daddy dearest waiting to pop it open again," Dean grumbled.

"We had better get looking," Sam said as he sat down in front of his laptop, fingers already flying across the keys.
_

With all the God searching that had been going on over the past few months Dean had forgotten how convenient it was to have a celestial connection when searching for demonic activity. In under an hour Castiel had located the Asmodai and had assessed the size and threat of his rapidly growing army.

"Okay," Sam said, processing the fountain of knowledge Castiel just poured on them immediately upon popping into the middle of the room. "So the Asmodai is collecting an army in Montana?"

"Yes. I have seen his followers in an abandoned warehouse facility in an isolated town. We have to move quickly. Every moment we delay our enemy gains strength."

With that the trio piled into the Impala with Dean tearing down the highway.
_

It wasn't often that Dean Winchester was caught off guard. In fact Dean Winchester was never caught off guard. It was because of this that Sam could hardly register the events that were taking place before his eyes. Sam watched as his brother fought the super-demons with practiced skill, he and Castiel working like two parts of a machine; cutting and stabbing then tossing weapons to each other, one just used and the other covered in a fresh layer of angel blood. Sam was assigned to watch from the outskirts and see if he could locate the Asmodai. He clutched Castiel's silver blade, which was doused in the divine blood. Castiel theorized that the holy blade combined with the blood would be strong enough to kill the leader. If Sam could locate the Asmodai while Dean and Castiel occupied the followers they may have a chance of killing it.

Everything was going to plan. Even in their more powerful state the demons had still not been able to inflict a wound on either Dean or Castiel. There were only a few members of the following left to kill. Castiel was engaged in a particularly aggressive battle with one of the demons who had managed to block the angels killing blow and hold him off by sheer strength. Dean on the other hand had just stuck his knife in the belly of the opponent he was facing.

"Cas!" he yelled as he saw the demon knock the weapon from the angel's grip and send it skidding across the concrete floor. Cas turned to Dean just in time to catch the knife Dean threw to him. He ran the blade across his palm to cover it in blood and buried it in the chest of the demon.

Dean began to walk towards the angel, "Alright now where is the-"

He was abruptly cut off as a demon snuck out from behind some of the abandoned crates and seized him from behind, throwing him to the ground and raking his clawed fingers through the flesh on Dean's chest and abdomen. Sam saw it like it had progressed in slow motion and before he could stop himself he was sprinting towards his brother and throwing the angel blade through the air.

The blade flew, turning end over end, until it embedded itself hilt-deep into the back of the demon attacking Dean. Castiel was right in his hypothesis about the blade. As soon as it buried itself into the demon, the creature burst into flame; a sparkling white flame that was so bright it was painful to look at. After the fire died out there was nothing left except for the discarded blade, cold and clean on the ground beside Dean.

Sam was pulling Dean up and helping him lean against a row of crates in an instant. "Dean!" he said breathlessly, taking off his jacket and pressing it against his brother's chest, "Dean…you 're okay…you're gonna be fine."

Castiel was at his side, "Sam, try to slow the bleeding," he crouched down and picked up the angel blade, "I will find the Asmodai." He slid the blade across his inner forearm, covering it in blood while ignoring the searing pain the weapon gave him.

"Monstra te!" Show yourself Castiel commanded, the ancient Latin sliding off his tongue. A shadow moved in the corner of his vision and he turned toward it, blade at the ready. A raspy laugh echoed through the warehouse and for a moment Castiel felt a cold wave of fear rise up his spine. His thoughts went back to centuries before when this creature had created an army that took out angles by the hundreds. He tightened his grip on the angel blade, swallowing thickly.

Suddenly the creature appeared in front of him, circling him slowly like a predator eyeing his prey. Another bout of cold laughter escaped from the mutated mouth, exposing razor-sharp teeth.

"Tibi non habent potestatem Filius Caelo." You have no power Son of Heaven, the creature rasped as he looked at his opponent.

"Potentia satis eiciendi daemoni!" Power enough to cast out devils Castiel yelled as he lunged towards the Asmodai.

The creature dodged Cas's first blow with a movement that gave the illusion of a nearly liquid spine. In the same movement he curled around and slashed his claws towards Castiel's face. The angel ducked and turned, attacking from behind the demon.

Sam watched from his brother's side, as he pressed his jacket to Dean's chest. It was impossible to tear his eyes away from this battle of Titans. Both moved with incredible speed and flexibility…he couldn't even tell who had the upper hand.

"Sammy…" Sam turned his attention to his brother. "I don't think…" he coughed blood, grimacing and swallowing thickly.

"Oh no you don't Dean," Sam said desperately, "Cas will be able to help you just need to hang on."

"Burns…" Dean choked out. He coughed again and a moan escaped from clenched teeth. Sam pulled back Dean's shirt to reveal jagged slashes that showed inflamed skin and black poison seeping through the veins around the wounds.

"Come on Cas…" Sam said quietly.

At that moment a fierce howl rang through the warehouse. Sam turned to see the Asmodai staggering backwards with the angel blade hilt-deep in his chest. Castiel was standing, hunched in front of him breathing heavily. The Asmodai wrapped a clawed hand around the blade and pulled it out slowly and let it clatter to the ground.

"Iam precor Angelus," Pray now, Angel the creature growled, taking a faltering step towards Castiel. Castiel closed his eyes and stood erect. Sam could swear Castiel was starting to glow. He doesn't have this power…he is cut off from Heaven Sam thought. However when Castiel opened his eyes they glowed white, so bright you could hardly look at them. Sam watched in awe as the shadows of Castiel's wings unfurled themselves across the wall behind him.

The Asmodai let out a feral growl and lunged towards the angel. Castiel threw his hand up in an almost robotic motion and white light burst from his palm and collided directly with the stab wound. Immediately the Asmodai burst into a pillar of white flame and as soon as it happened it was over. Sam was left in an unnatural darkness with spots in his vision.

"Smm-y…" Sam locked eyes with his brother just to watch him start to seize.

"Dean! No! It's over, we killed him. Now just hang on…please…" Dean's eyes rolled back into his head and he went limp.

"No no no no…Cas! CAS!" Sam yelled in desperation.

"Move!" a gruff demand sent Sam scuttling to the side as the angel fell to his knees in front of Dean. Cas pulled Dean's jacket off of his shoulder and in one swift movement he tore the t-shirt underneath from the cuff to the neckline. The fabric fell away to reveal the hand-shape scar adorning Dean's shoulder.

Cas cupped one hand gently around Dean's cheek and placed the other hand over the scar. He closed his eyes and started to mutter in Enochian and Sam watched, transfixed, as the black poison began to collect and travel, through Dean's veins, towards the scar on his shoulder. Dean's brow furrowed and he tried to pull away but Castiel tightened the grip on Dean's shoulder. Sam saw sweat break out on the angel's forehead and his voice broke slightly as he continued.

Dean was sure he was burning. He kept his eyes tightly closed…terrified of what he would see if he opened them. The acrid scent of sulfur assaulted his nose. 'No' he thought, 'This can't be happening…I can't be back here…it isn't possible.' However the more he denied it the clearer it became. The heat, the sulfur, and he could hear the screaming of tortured souls. He opened his eyes. He was back in hell.

As the poison collected by Dean's shoulder he began to fight in earnest. Castiel's voice rose as he worked to keep Dean under control. A soft light began to emanate from the angel and Sam heard a ringing begin to build in his ears. Dean began to jerk like a man possessed and all Sam saw was light and movement and all he heard was a high-pitched ring and the Enochian chant.

'Dean.' Dean turned his head towards the familiar voice. Standing amidst the smoke and flame was Castiel, glowing slightly and holding a hand out to him. 'Dean. Take my hand.' Flames erupted from beside Dean and he was overcome with terror. 'Cas?' he yelled. Smoke burned his eyes. 'CAS?' He felt someone grab his shoulder and he turned to see Castiel, inches from his face, his blue eyes burning into him with determination. Cas placed his hand on Dean's cheek. Dean felt peace wash through him and the pain he was feeling began to fade. But something was wrong…he looked at the angel and watched as Cas started to shake. 'No…' he said quietly starting to realize what the angel was doing for him. 'Cas stop…don't do this…' but he could hardly fight it. He could feel the evil leave him; the heat began to fade and the smoke began to clear. He felt tired and peaceful…his eyes started to close on their own accord.

Just when the crescendo of sounds and light peaked there was absolute silence and for the second time that day Sam was suddenly bathed in an unnatural darkness. His eyes immediately went to his brother and Sam watched as the black poison transferred itself from Dean's shoulder and slid through Castiel's veins to his chest where the white button-down shirt the angel always wore started blossoming in red…a perfect mirror of Dean's injuries.

Castiel groaned and pulled back, his hands shaking. The moment the contact stopped Dean's eyes popped open and he took a breath like a man who was drowning. He immediately reached out and grabbed Cas as the angel fell backwards. He pulled Cas against his chest.

"Damn it Cas…" he said as tears welled up in his eyes. Castiel started to tremble and cough, his teeth getting stained red with blood. "How could you do this?" How could Dean Winchester, a selfish sinner deserve the constant sacrifice of an Angel of the Lord?

Cas looked Dean in the eyes. "You are it Dean," he said quietly.

"I am what, Cas?" Dean barely asked around the lump in his throat.

"My most amazing miracle."

Dean closed his eyes, allowing a tear to escape between the lids. He pulled the trembling angel close and placed a kiss on Castiel's forehead. The angel clutched Dean's jacket as he was wracked with coughs. Dean wrapped his hand around the back of Cas's neck.

"One in ten can survive this?" He asked looking pleadingly into Cas's eyes.

Cas nodded, "Yes," he said weakly.

"You had better fight this," Dean said and the conviction in his voice was so strong it could almost be felt. "You fight this, you hear me?"

Cas gave him a faint smile. "Of course. Anything for Dean Winchester." His eyes fluttered shut as Dean picked him up and carried him to the Impala.

FIN

A/N: My very first attempt at Destiel! What did you guys think? The Latin was from Google Translate so if it was totally wrong blame them :P Also I don't have anyone to edit my work so I am really sorry if there are any typos or grammar mistakes. I read through it a few times but you can never catch everything.

I hope you enjoyed this! Please review!