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how to be a demon

Summary:

Ever find yourself waking up in the middle of an alleyway after an accident with no memory of how you got there? Ever been chased by a crazy hot guy with a sword, or find yourself accidentally stumbling into the dark and complex supernatural world of demons? Well, if you have then you've come to the right place. Because that's exactly what's happening to Choi Beomgyu; an ex-normal college student.

The process of becoming a demon isn't easy, especially when you're basically the key for balance between good and evil. But with some determination, good practice, and a mischievous demon guardian at your side, you can master the art of demonic life in no time! (Along with the crazy prophecies, magic, hunters, millennia-old feuding, and romance(?) that comes with it)

Chapter 1: step 1: wake up in an alleyway

Notes:

hello~
this is my first story on ao3 and also my first attempt at a supernatural au. i thought about yeonjun and soobin being demon slayers with swords and said "hell yeah".
Hopefully this goes well, enjoy!
(warning tho: this has some blood and violence, nothing too gory i think)

(See the end of the chapter for more notes.)

Chapter Text

step one: wake up in an alleyway


~ yeonjun ~

They always smelled like sulfur. The smell was sharp and intoxicating, and burned the airways insides like poison. It was the easiest way to sniff out a demon, but it takes time and training to be able to desensitize and recognize. Gripping the cool, metal blade in his hand a little harder, Yeonjun made his way through the obscure darkness. He didn’t need light to know that it was here. There was always something about that eerie, abandoned warehouse at the end of the street and on the verge of society, that attracted them here like moths to a bright flame. He wasn’t exactly sure why, but it made his job a hell of a lot easier.

Yeonjun stiffened at the sounds of sharp whispers, carried by the wind and blowing past his ears. A metallic whirring sound broke the silence as he unsheathed his blade, so fast that he felt the wind whipping around it. The sulfurous smell was starting to create an itch at the back of his throat that he couldn’t scratch, and he knew that he needed to be quick. Blade poised in an elegant but defensive position, Yeonjun continued to move through the dimmed darkness of the abandoned warehouse. He had walked a couple of more blocks, before the sulfur odor suddenly disappeared, along with the high-pitched whistles. He paused, his eyebrows drawing together in confusion, his full but petite lips set in a firm grimace.

And then, the odor was overwhelming.

Without hesitation, he swung his blade, his body twisting with the force of the swing as it slashed into the figure behind him. The figure was as dark as the space around, them except for one strikingly noticeable feature; its blood-red eyes. It had stepped back at the last second so that the blade had only sliced its arm, and let out an ear-splitting shriek, before grounding out a deep, throaty snarl as it swung for Yeonjun with its long, jagged claws. Yeonjun expertly dodged each blow, matching them with a blow of his own, swinging the blade and just missing the shadowy figure’s chest each time. He gasped when he felt cold, sharp nails wrap around his ankle and wrenched him toward the ground. His back slammed against the solid surface, and he hissed a curse as pain bloomed in his lower spine, before mentally pushing it away.

The demon’s crimson eyes gleamed with sadistic delight as it let out a mocking sneer. “This is the great Hunter? Slayer of the ghouls and demons that haunt and roam this earth? I am unimpressed.” 

Yeonjun tried to reach for his blade that was knocked out of his grasp from the impact, but another clawed hand had clasped his shoulder, nails piercing through the fabric as the figure kept him rooted to the ground. He swore again under his breath, his mind racing a mile a minute, as he stared into the crimson eyes of the monster.

“What are you planning?” Yeonjun demanded through gritted teeth. “Why do you keep coming here?”

The figure tsked lowly. “You should be more concerned about begging for your life.”

He spat into its crimson eyes. The figure reeled back, a growl of disgust rolling through its chest before it snarled again. The crimson eyes narrowed dangerously, and sulfur was beginning to choke up his lungs. The nails submerged into his shoulder were quickly released, only to wrap around his throat tightly. Now the burning sensation inside his throat was amplified, as strangled gasps escaped his mouth.

“I want to see the life drain from your eyes, you filthy human," it hissed at him, its hot breath fanning his face.

All Yeonjun could respond with was gasps, purposely making sure that they were loud and theatrical, so the monster wouldn’t notice that his injured arm was slowly reaching for the discarded blade. Even in the dim darkness, he could feel his vision becoming splotchy, his head heavy and chest on fire as the monster continued to strangle him. 

Just a little further, dammit! Yeonjun thought frantically. His fingers could almost touch the cool metal.

His heartbeat slowed, and he could feel the heavy numbness began to wash over his body, threatening to drag him into oblivion. His fingers brushed against the metal again, and another time, before he finally found his grip, and skillfully maneuvered the blade so that it came through the shadowy figure’s chest. Another loud, wet-pained howl came from the figure as it fell onto its back, and Yeonjun quickly lunged to be on top of it, hands wrapped around the handle of the blade. He could see the murky black liquid from the figure gushing out and dripping down his face and blade, and at the contact of its blood, the blade glowed a pale white softly. But he didn’t insert it deep enough to kill it, not just yet, he still needed answers.

“I’ll ask again,” Yeonjun said firmly, twisting the blade and eliciting another painful screech from the monster under him, “what are you planning?”

“You will never know,” the demon spat back venomously, “just know that you and your vile kind’s days are numbered.”

Yeonjun gritted his teeth at the retort, before pulling the blade out of its chest, only to plunge it back into its chest with all his force. The shrieks rose to an almost unbearable level, and a burning stench filled the air as the shadowy body under him dissolved until there was nothing left but the sulfurous smoke.

And then, silence.

He didn’t realize he was holding his breath, until the fiery sensation in his lungs surged inside him, and he took heavy labored breaths. Once his breathing returned to normal, Yeonjun stood to his feet, the glowing blade in his hand fading back to its dark monochromatic color. 

He had been retracing his steps in the long, dark hallway when something began to vibrate loudly in his pocket, the noise echoing in the empty hallway. Yeonjun stopped to pull his buzzing cell phone out of his pocket, before placing it against his ear.

“Is it taken care of?” A deep, masculine voice asked on the other end.

“Yes, it’s done,” Yeonjun confirmed, wiping the blood off his blade on the wall before sheathing it.

“Took you long enough,” the voice snorted on the other line, “I thought I was gonna have to send backup to come save your ass.”

The blonde rolled his eyes playfully. “Shut up Soobin.”

Soobin snickered for a moment. “Did you at least get any info out of it?”

“No,” Yeonjun replied, huffing indignantly, “that’s the tenth one I’ve found there, and still nothing.”

“Hmm,” Soobin murmured curiously, “This must be something big if they’d willingly die before they talk. I’m almost impressed, lower-level demons are usually rogues or unorganized factions.”

“Doesn’t sound impressive to me,” the blonde muttered, “we need to find out what they’re planning so we can stop it.”

“We do,” Soobin agreed, “but for now, we need to regroup. Report back to the headquarters immediately.”

“Yeah, yeah.” Yeonjun said flippantly, “See you there.” He hung up the phone, pushing through the exit doors, and taking in the fresh air of the night. Finally, something other than sulfur.

The blonde walked out of the abandoned building, strapping the sheath under his long, black baggy coat as he shoved his hands into his pockets. His boots made a heavy thump against the pavement as he walked back down the street and toward the buzzing nightlife of the city. The final words of that demon were playing in the back of his mind, but he couldn’t seem to make sense of them. They had word from headquarters that the demons were up to something, it was something big, and he just wished he could figure it out. He didn’t like how long it was taking him and Soobin to complete this particular mission.

A frown settled on Yeonjun’s pouty lips, the sounds of heavy wind and cars kept him company as he approached a more populated area. He groaned at the dull sense of pain that pulsed from his shoulder, that demon sure put up a good fight. He already knew there were going to be unpleasant bruises on his left ankle and around his neck, and he definitely wasn’t looking forward to hearing Soobin clowning him about them later on. His stomach grumbled suddenly, alerting him to the fact that he hadn’t really eaten anything substantial for the past five hours.

Great. 

He rounded another corner, thinking about his favorite convenience store when he heard a strange sound. It was a faint sound, but due to Yeonjun being a trained hunter, he was able to pick up on noises that would otherwise be imperceptible to an average person. It sounded like someone was coughing, and by the strangled, hoarseness of it, it sounded painful. It was accompanied by pitiful whimpering, and Yeonjun paused in his steps. It sounded like someone was in trouble, and without another thought the blonde took off towards the direction of the noise soundlessly.

He rounded another block, the coughing and whimpering becoming much louder. It was coming from a small alleyway in between two buildings, and the blonde started moving towards the alleyway when he suddenly froze in his steps, his body naturally tensing in response. He smelled sulfur. That meant there was a demon involved, this could be an attack. He gripped the handle of the blade under his coat, debating on if he should call Soobin to let him know. He snapped into action when he heard another pain-filled whimper, and Yeonjun rounded the corner, whipping his dark blade out with an almost inhuman speed. 

He expected to see some dark, terrifying monster terrorizing an innocent person. He was a little bit thrown off by the sight of a young guy kneeling in the middle of the alley. His face was hidden by his dark hair and hands, his shoulders shaking as he continued coughing. Yeonjun’s eyes widened, half in shock and half in confusion. He didn’t look like he was in any immediate danger, but the smell of sulfur was still strong in the air...although it smelled a little differently than it usually did. It was tinged with something else, diluted enough that it didn’t burn Yeonjun’s lungs when he inhaled the air. He scanned their environment around them, checking for any monsters, but when he couldn’t find anything he frowned. Something was definitely here, there were black stains all over the ground, and also on the guy. Could he have been attacked, and the demon left before he showed up? That sounded plausible to him.

Still alert, Yeonjun glanced at the guy on the ground. He looked young, probably around his age or slightly younger. He was still coughing and whimpering, every heave sounding more painful than the last. “Hey, are you oka-”

Yeonjun’s words were cut off by the sounds of the guy retching onto the ground, staining it with more black liquid. Yeonjun froze again, his eyes widening. It was silent for a moment, the guy stiffening at the sound of another person, before slowly his hands fell away from his face. Hesitantly, he looked up at him, and Yeonjun stared into crimson eyes.

Demon eyes.

He was one of them!

Yeonjun’s heart jumped into his chest as he stared at his eyes first, then the sharp veiny nails, and the black blood that spilled from his lips as he coughed again. The shock flooded his systems for a moment, before he pushed it away and regained the trained focus and determination he acquired after years of demon hunting. 

“I-” The guy choked on his own words for a moment, his eyes widening when they darted to the blade in the blonde’s hand, “w-wait, no-”

Yeonjun lunged at him, his blade swung with fine precision as he aimed for the demon’s chest.


~ beomgyu ~

“Beomgyu...Beomgyu, wake up!” Was the voice he heard, pulling him out of his sleep.

Beomgyu opened his eyes groggily, before sitting up immediately at the sharp burst of pain that erupted from his chest. His vision cleared as he groaned, before glaring at the assailant who stood by his bed, arms crossed.

“What did you hit me for, Taehyun?” The dark-haired boy groaned, rubbing his chest.

Taehyun remained unfazed. “We have a problem. It’s urgent.”

“What?”

“We’re out of ramen.”

Beomgyu groaned with a roll of his eyes. “Are you serious? That’s what you woke me up for?”

“I’m hungry,” Taehyun stated, with a frown that was borderline a pout.

Beomgyu squinted at him. “Okay? Go get some ramen then.”

“I can’t, I have a paper due in twenty minutes.” The redhead says, “can you run out to the convenience store and get me some?”

“I was literally sleeping,” Beomgyu complained.

“Please, I’ll owe you one.” Taehyun pleaded, “I really need to finish this paper, and I’m starving. I feel like I’m going to pass out. And if I pass out then I’ll miss Professor Lee’s deadline, and then I’ll get a zero on this stupid paper I’ve been writing for the past four hours, then I’ll fail his class, and then I’ll-”

“Okay, okay I get it!” Beomgyu said, pulling the covers off of himself as he regrettably got out of bed. He glared at the younger, “you will owe me for this.”

Taehyun just gave him a satisfied smile, handing him the money for the food before going back to his desk where his laptop sat. Sometimes, Beomgyu did not enjoy having his best friend as his roommate, these were one of those times. Begrudgingly, he shoved on some pants and slipped into a warm, oversized hoodie. He grabbed his keys and ID to their room and glared at Taehyun one more time as the redhead waved him goodbye.

That was how he ended up at the convenience store a couple of minutes away from their university, at almost eleven o’clock at night. He grumbled to himself as he walked through the aisle, getting two bags of spicy ramen (Taehyun loves it spicy) and a couple of other snacks before heading up to the front to check out. The girl at the front looked just as dead inside as he felt, and he found a small bit of solace in that. She rang up the items and gave the price, Beomgyu fished Taehyun’s money out of his pocket and put it on the counter.

He cursed as he felt the wind blast his face as he opened the door, and Beomgyu grumbled to himself again, thinking about how nice and warm he could be if he was in his bed right now. He sighed to himself, walking down the sidewalk as he made his way back to their school. Bored and tired, he decided listening to music wouldn’t hurt as a way to pass the time. He put in his earbuds, humming to the melody of the song softly as he walked. 

He was so engrossed in the song that he did, in retrospect, one of the dumbest things he’d ever done before.

Beomgyu crossed the street, nodding along to the song. He didn’t hear the squeals of the tires or the blare of the horn from the car that was quickly approaching him. He didn’t notice anything until he looked up by chance, seeing an old man on the other side of the street waving and yelling at him frantically. Beomgyu’s eyebrows furrowed to showcase his confusion, before his gaze snapped to his right, staring at the pair of blinding white lights that came barreling towards him. He remembered the way his hair stood on end; the frozen horror that was on his face, and the burst of pain that seemed to come from everywhere at once. The sickening crunch of his body as it flew into the air, the ground pulled from under his feet, before he was harshly re-acquainted with it as his body slammed into the ground. 

He remembered feeling the searing pain racing up every nerve of his body, every shallow breath he took made it feel like he was trying to breathe fire. His head was pounding, and his ears were ringing. The shouts and screams of the people around him were all distorted around him like everything was moving in slow motion. He could feel something wet and warm pooling below him, and Beomgyu wheezed in agony. The pain was unbearable, and he could feel his vision beginning to get splotchy around the corners. But despite his blurry vision, he remembered seeing a young boy appear in front of him. He didn’t look like he was much older than him; he had long dark locks and wide eyes that would’ve shone with an aura of child-like innocence if it wasn’t for the pupils that were glowing red.

Red?  Beomgyu’s brain was a little foggy, so maybe he was hallucinating this because he could feel himself moments away from losing consciousness. He looked away from the strange boy with glowing red eyes and up to the night sky, it was a full moon tonight. He heard the boy’s low voice as he spoke, chanting in a language that Beomgyu couldn’t understand, before his consciousness slipped away.

And everything went dark.


Beomgyu woke with a start, jolting up immediately with a gasp. His heart was pounding in his ears, and he grasped his chest as he frantically looked around. It took him a moment to realize he wasn’t bleeding out in the middle of the street, but in a dark alleyway- 

Wait. 

He was alive?

Beomgyu stopped panicking for a moment, really taking in his surroundings again. He had no idea where he was, but he was alone. He looked down at his clothes, which were still tattered with blood and dirt. He lifted his hood, peering down with a mix of shock and confusion at his smooth skin. Not a scratch in sight, and it didn’t feel like his lungs were burning every time he took a breath—actually he could breathe normally. 

“What the hell?” Beomgyu mumbled out loud. His head still felt a little fuzzy, but other than that, he was fine.

But that was the problem. Wasn’t he just in an accident? He shouldn’t just be fine like this. Not that he’d rather be in excruciating pain, but none of this felt right to him. He pinched himself on the side, just to make sure he wasn’t dreaming. Something wasn’t adding up, how did he get here, with no injuries? The pain from the impact of that car was way too real to be just his imagination. And even if it was some wild, terrifying dream, shouldn’t he have woken back up in his room?

There was a soft crackling sound, as if someone stepped on a twig, and Beomgyu’s head immediately snapped in the direction. “Hello?!” He called out frantically, “is someone there?”

There was no response. Beomgyu was alone in this dark alley, but despite the darkness, he didn’t have to squint to see like he usually would. His vision was perfectly clear. 

“I need to get out of here,” he mumbled to himself, checking his pockets to see if he had his phone. When he couldn’t find it, he looked around himself for a few minutes, before finally giving up and deciding to find the nearest payphone so he could call Taehyun. 

When he tried to stand up to leave, he could feel a sharp crack of pain swarm inside his head, so strong that he collapsed to his knees. Beomgyu let out a painful, feeling something twist and burn inside his chest. One moment he was perfectly fine, and then the next he could feel himself throwing up blood. Or well, he thought it was blood, but when he looked down at the liquid that stained the ground and his clothes, he realized it was black.

What the hell?!

Beomgyu couldn’t stop coughing, the pain rising, but this was a different kind of pain from the one he suffered in the accident. This pain was white-hot and sweltering, it felt like his insides were heating up, and his blood felt like it was boiling. More black liquid spilled from his lips as he kept coughing, he didn’t know why and he couldn’t stop it. His body was acting on impulse, as if it was trying to purge something inside of him. The pain only worsened the longer Beomgyu coughed, his sides started to hurt and his throat burned. He blinked back tears that pricked the corner of his eyes, and they widened in terror when he saw his hands. His fingers were changing, ugly veins pulsing around them as his nails grew longer and sharper. 

Panic started to bubble up in his chest, and Beomgyu bit down on his lip to try and stop the coughing. He only gasped when he felt pointy teeth prick his lip and panicked even more. What was happening to him? Why was his body doing this to him? Beomgyu didn’t feel like himself anymore, he felt like he was turning into something darker, something wicked. A memory of red eyes flashed inside his head for a moment, but the memory was so murky that he couldn’t understand it. Beomgyu started to cry, the tears in the corner of his eyes falling and mixing with the blood that kept spilling from his lips. He buried himself in his hands, whimpering. He thought that he was going to die here, all alone where no one would be able to help or find him. 

Then he heard the sounds of heavy footsteps that were coming his way. Soon enough, he could tell someone had arrived to his rescue. They were panting heavily from the run, they stopped moving for a moment, but then Beomgyu let out another painful whimper and the footsteps resumed. 

“Hey, are you oka-”

Beomgyu threw up again, obsidian liquid spilling past his lips at an alarming rate. He coughed again afterward. It was silent after that. Shakily, Beomgyu willed himself to lift his head from his hands, his whole body was shaking from the pain. 

Beomgyu looked up to see perhaps the most beautiful guy he’s ever seen before staring down at him. He had long tawny hair that was messily pushed back, wide dark eyes, and full pink lips that were currently arranging themselves into a grimace. The shock left his eyes and was replaced with something darker.

“I-” Beomgyu tried to speak but his throat was still strained from everything. It was just then that he noticed the long-ass weapon the blonde guy was holding. “W-Wait, no-” He nervously stammered.

The blonde cut him off as he lunged at him, and Beomgyu’s heart sank. 

Notes:

hope you guys liked it! please leave a comment if you did, tell me what you think :)