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English
Series:
Part 1 of Monarch among the beasts of Men
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Published:
2023-06-21
Updated:
2025-04-13
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147,155
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40/65
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This demon in Disguise

Summary:

Being a demon isn't easy, nor is trying to find a place in the world while struggling with inner turmoils and forgotten problems.

Genya Shinazugawa's life is turned on its head by a man named Muzan and he's determined to break free from the demons control while also keeping his loved ones safe.

With Sanemi, his brother, being a person Genya wants to try and forget, hurling himself into the world of demon slaying, Genya comes to find him in a far worse state than he ever imagined and both brothers have to find it in themselves to mend their broken relationship while struggling with new problems.

 

(New summery cause the last one was ass, this one might be too but it’s better 😅)

‼️‼️ This story will be under construction for the summer months and now! So updates on any other fics will be paused, sorry for the wait! This fic will be fixed of any spelling mistakes and plot holes, as well as cringe writing.

Have a great spring/summer!!!

Chapters finalized 7/37

Notes:

(See the end of the work for notes.)

Chapter 1: Agony

Notes:

(Chapter has been edited and checked for spelling errors)

⚠️ warning! If you did not read the tags, please do! This fic is rather graphic in terms of injury and death! If you are sensitive to these things you have been warned (:

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

Chapter Text

 

Genya glanced back at the door for what had to be the tenth time that night, heart beating strangely as he bit the inside of his cheek and shared a look with his siblings that all held nervous stares. All the lights were on and they weren’t sleeping like they should be, too fidgety to even try to rest.

The problem was, that their mother had not come home and it was getting quite late.

Genya grit his teeth, bouncing his leg to try and let out the nerves that had built up after waiting for at least two hours. His eyes felt sore, struggling to stay awake, yet his mind was racing. Where was she? Was she okay? Did something happen? Were all questions he’d asked himself probably hundreds of times in the span of a few minutes.

Genya was always left unanswered.

His mother worked often. She had to in order to keep food on the table and make sure everyone had clean clothes. She worked from early in the morning until the sun set, and after, made time for Genya and his siblings so they didn’t feel neglected.

It was rare. Incredibly rare and unexpected by everyone that she had not come through the door yet, and didn’t seem to be coming anytime soon if the quiet of the night had any say in it.

No wind greeted Genya’s ears. No late night drunks, or stray dogs knocking over garbage cans to get their fill, not even the crickets and late night peepers started the melody of their song.

It sent a shiver down his spine, tense shoulders becoming knotted as they stayed stiff for too much time.

Sanemi, Genya’s older brother, let out an audible sigh, eyes filling with fire laced with deep dread. He clenched his fists, rising to his feet and gaining the attention of the younger ones, looking at him with curious eyes.

 “I’m going to go look for her.” Sanemi declared, expression hard.

Genya’s heart twisted and he widened his then darted them back to the door, unsure if he should stop his brother, Nemi, or if he should keep his mouth shut. Sanemi was stubborn, and looking at the emotion painted on his face, Genya’s opinion would not hold any weight. So what would even be the point?

Genya sighed.

 “Genya.” Sanemi called, drawing him back to the present.

 “Watch over everyone, okay? I’ll be back soon… with mom. I’ll be as fast as possible, I’m sure she’s fine.” Sanemi reassured, quickly breaking eye contact in favour of fidgeting with his sleeve, and working his jaw.

Genya paused, then nodded. Sanemi walked over to the kitchen, and grabbed something, slipping it under his clothes before Genya could catch a glimpse, the only thing he managed to see being the glint of light from the object. Sanemi turned and opened the door, fresh night air making goosebumps appear on Genya’s skin.

Genya flinched, scrambling back as Sanemi reacted, letting out a gasp and stumbling, nearly reaching for the object he’d hidden.

Mother was at the door, scaring all of them… she hadn’t been there a second ago…

Genya let out a strained breath,holding his chest, trying to calm his thundering heart. Sanemi did the same, looking shook but alright.

 “Oh dear, did I scare you? I apologize.” She sympathized, puting a hand on Sanemi’s tense shoulder.

 “We’re just glad you’re home. You were gone a long time. Did something happen?” Sanemi asked, concern lacing his every word.

Genya got to his feet, coming up at Sanemi’s side.

 “Nothing you two need to worry about.” She smiled, something oddly sinister to it. Her eyes gleamed strangely, and Genya tilted his head looking at her, something about the way her words came out and her smile making alarms go off in his head.

They were faint. But still there.

 “Are.. are you okay mom?” Genya hesitated, swallowing thickly. His mothers brow raised in response, smile faltering.

 “Don’t worry sweetheart, I can assure you everything is fine, it’s just been a long day.” Was her response as she lightly hugged him, something that once brought comfort and warmth, now leaving a chill on his body, and his skin crawling like he had touched something made of a million nasty bugs. Genya brushed it off, gaze landing on the floor.

His mothers embrace was snug, her arms pressed firmly around his body. Genya hugged back, the action bringing no relief.

 “Now everyone to bed. It’s way past your bedtime. How are you meant to wake up tomorrow at a reasonable hour?” She questioned, crossing her arms and gaining tired agreement from everyone. 

After all the lights were turned off, and everyone was comfortable in their futons, Genya tried to ignore the fact that his mother had sent them all to bed without dinner…

She never did that, and Genya’s stomach growled knowing it too.

No matter how hard Genya tried to sleep the thought plagued him. Mother was acting weird, really weird. Her voice seemed off, the way she talked and moved. The way her hand rested on his shoulder and the way she hugged him. She felt like she was an actor struggling to keep in character, a wolf in sheeps clothing. But… she was there, with him. His mother…

An off day at work maybe…

Finding some sort of closure in that thought, Genya tried to ease his mind to sleep, promising himself everything was fine. Even so, sleep evaded him like a plague. Grumbling, Genya tossed and turned, trying to get comfortable enough to fall into slumber, but his efforts were in vain as the night went on and a sickening feeling rested at the bottom of his stomach, twisting uncomfortably. 

Genya tried to ignore it, he really did, thinking maybe he’d just eaten something bad, or his growing hunger was making him feel sick, but his instincts were telling him that he had to be alert, so he was constantly opening his eyes and looking around. His stomach dropping every time, fearing he’d see something other than his sleeping family.

He avoided thinking about it too much, more relieved that his mother came back safe and sound, but the nagging wouldn’t go away so he kept his eyes closed and hoped he’d be able to get some sleep.

An hour later, Genya’s eyes fluttered open, and he groggily rubbed the sleep crusties from them, realizing he had managed to fall asleep just like he’d hoped.

He sat up in his futon, stretching his back as he let out an exhausted yawn. His unfocused gaze drifted to his sleeping family, his younger siblings letting out small snores,  messy hair pointed in all directions. He smiled seeing everyone so content.

Genya then began to think. Wondering what woke him. He didn’t need to go to the washroom, and he wasn’t hungry (anymore), nor did he fall victim to a nightmare.

His questions fell to an abrupt stop when a shiver crawled down his neck and back, eyes widening as he felt eyes on him. Genya felt the dread he’d felt earlier resurface, clawing at his insides as he slowly turned his head.

His gaze landed at the door, and there stood a figure.

A beat of silence.

 

 “mom?”

 

Genya called and he went pale remembering that no, that couldn’t be his mother because she was still in her futon, fast asleep…

Right?

Genya made the mistake of glancing back at where his mother was meant to be fast asleep, only to see she wasn’t there, his stomach dropping, then looking back at the figure. 

It was gone.

Genya’s heart was beating in his ears. It was all he could listen to as thoughts swirled in his head.

 If his mother wasn’t in her futon… and there was no figure at the door any longer…who was the figure and where was his mom? Genya asked himself, beginning to find it hard to breath.

Whoever the figure had been, was tall, too tall to be his mother and it’s aura just screamed “danger” his stomach twisting and turning as he shakily looked around, heart in his throat.

Genya’s eyes stayed firmly on the door, realizing it was halfway cracked open, sending cool night air to ruffle his hair, a shiver running throughout his body.

His hand drifted to Sanemi’s shoulder.

“N-nemi…Nemi wake up”

Genya was still looking at the door but he was silently shaking his older brother.

“Mm what is it Genya…m tired” he slurred out, drifting back off almost instantly. Genya shook harder heart spiking and sweat forming on his hands and back, effectively waking up his tired brother.

“…Genya? What is it… What’s wrong?”Sanemi urged. Blinking the tired away from his eyes, gaining a more alert gaze.

Genya’s words were stuck, his thoughts unable to form proper words as he froze up. A noise came from outside and he was effectively silenced, the interruption more helpful than Genya ever seemed to be. Sanemi’s head swivelled to the door, gaze piercing and eyes wide. His jaw grew taunt and he got to his feet, the last remnants of sleep fading from his brothers form. Concern. It was all Genya could see growing on Sanemi’s features.

 “Genya… where’s mom?” Sanemi asked, yet the question did not seem directed at him, Sanemi gaze trained on the door, and the claw mark that rested on the paper wall.

Genya’s eyes followed Sanemi’s lead, and he froze, ice filling his veins.

 “Genya. Get our brothers and sisters out the back, and hide.” Sanemi ordered, his eyes locked onto red ones, planted on their mothers face, a smile filled with fangs, hungry and close to pouncing for their throat’s. Sanemi swallowed, pulling a cleaver from his clothes.

That was not their mother standing in the moonlight.

Genya wanted to say no, he wanted to tell Sanemi to come with them, but he caved, lip quivering and voice completely leaving him. He nodded, defeat evident in his eyes. Genya rushed to his younger siblings, the five of them deep in slumber. He shook them awake, picking up the youngest, and helping the others still half asleep to their feet.

 “Genya? Why did you wake me up?” One of his siblings whined, yet he couldn’t answer them, staring one last glance at Sanemi, seeing his shaking hands, and tense form, before pushing his siblings out the back door into the dark night.

 “Run! And don’t stop until you get to city!” Sanemi cried, his voice more frantic than Genya had ever heard it, as fast footsteps came thundering in Genya’s ears, turning away with great difficulty and forcing his siblings to run. Genya then felt something at his back, the booming sound of wood breaking apart and a body getting knocked to the side made tears well in his eyes as his legs complied to his command and he dashed forward with his siblings in front, the thing behind him preoccupied with Sanemi, his brothers screams of fury something he’d never forget.

Genya didn’t want to leave. God he didn’t want to. Yet his mind kept going to Sanemi’s voice that turned even more pleading in his head the more he thought of it. Sanemi told him to run, save his siblings from the thing outside their home, hungry looking and with the body of their mom. So he listened, because he was a damn coward, and all he could do was follow orders.

Ankther loud crash came from behind, and Sanemi’s fearsome yells died out, a sob escaping Genya’s lips as tears fell down his face, and his siblings slowed their pace, all trying to ask him questions.

 “No! Keep going! We need to-“ Genya was abruptly cut off, being wretched to the side by claws, slamming into a wall with an audible crack that rung out like nails on a chalkboard, a pathetic cry leaving his lips along with dark red blood.

Genya tried desperately to yell out to his siblings his face in the dirt, the scent of iron thick. He tried to tell them to keep running, don’t stop, even call out to Sanemi, as he bit back a sob but all he could do was gasp, each breath being smothered as he choked on blood. 

Genya was gaping like a fish out of water, eyes blown wide as he laid paralyzed on the ground, pain snaking and pulsing from his back.

His heart was beating so fast he couldn’t hear anything else, not even the screams from his siblings as he laid helpless, unable to protect them.

Unable to move.

 Even his fingers could only twitch as he drowned in crimson, his ears ringing and head filling with static.

 “Genya!” Sanemi screamed, voice hoarse, but he didn’t hear it.

Something then kneeled down in front of him, and his panic filled eyes met gleeful ones, belonging to a monster wearing his mothers skin, but it quickly changed appearance becoming that of a man.

It was tall, and glowing blood red eyes stared at him with nothing but coldness and sick joy. Whatever it was had fangs as it opened it mouth to speak. Genya didn’t hear what it said and his eyes focused on the sharp fangs that seemed to glow with the moonlight.

His vision became spotted and he used everything left in himself to move.

He didn’t so much as twitch.

 “Your efforts are useless little boy. Your back shattered into countless pieces when you hit that wall. I’m surprised you’re not dead yet actually. It’s impressive.” The demon taunted upon deaf ears.

 “When I found your pathetic mother on her way home I couldn’t help but take her place. A family easily forgotten is too valuable to ignore. The perfect place to make new demons…I wonder…” he paused, the only sound being gasping and gurgling as blood made it hard to take even a single breath. Genya would drown in his own blood before he fell victim to his injuries.

 “…I wonder if you could survive if I gave you enough blood, hm? There are plenty of bodies to consume, even that marechi is still alive, you could have some fun by hunting him. He’s injured enough that even a weak thing like you could make a meal out of him…” the Demon continued, no sympathy in his voice, only mocking.

Genya couldn’t hear any of it. His vision was fading, and the longer he breathed the less he felt like he was drowning. The less he tried and the more he slipped away.

He was cold.

then. 

pain.

 

Genya screamed, he howled in agony as something as hot as what felt like a thousand suns erupted into his veins. Fresh hot tears streamed down his face and he all he could smell was blood and dirt. He screamed and cried like a dying animal in the demons eyes, movement finally being given back to the wailing child on the ground, his hands digging into his hair, and legs curling to his chest before another spike of fire hit him, and he was sent writhing on the blood littered ground.

Muzan smiled.

 “I was generous to you. My blood will help you get stronger, you will see the disgust of being merely human, and welcome this change with open arms.” He laughed, eyes glinting and smile wide and fang filled as he turned on his heel, not caring as he stepped over dead the bodies of children and a barely awake marechi, clawing his way over to his screaming brother.

 “Pathetic.” Muzan snorted, striding past the boy and back into the night. As if he’d never been there at all, leaving nothing but carnage and a beast in his stead.

Sanemi used all the strength he could to drag himself over to Genya who was flailing on the ground, practically seizing as a scream so loud and full of agony deafened him. Sanemi grunted, his broken arm protesting, limp at his side. Sweat rolled down his forehead, mixing with the blood that coated his hair. The crimson liquid was on his hands, staining his clothes and falling from his mouth, dribbling down his chin in a steady stream. 

He didn’t care. Genya was so close, yet so far away at the same time. Sanemi tried his best to ignore the lifeless stare of one of his siblings, Shiyuu, dull eyes staring off at nothing. His heart wailed and his eyes stung, but he couldn’t cry. He couldn’t waste that energy. Not now. Not when he was so close.

 “G-Genya.” Sanemi begged, body failing him as he slumped on the ground, face in the dirt.

 “I…I’m sorry.” Sanemi forced out, Genya finally going quiet and limp, head rolling to the side as blood fell from his nose and his tears turned to blood. Sanemi let a cry leave him, curling up on the ground, his body starting to shake. He sobbed, unable to stop, clutching his arms so hard they bruised. All he could ask as a fog covered his mind, was why? Why did this happen?

Why did he get to live? Be the last one to die?

Sanemi drowned in an agony so guilt filled that even the street rats were repelled by it, and he let out one last cry of utter failure, chest heaving one more exaggerated breath, before his eyes fell closed, and Genya twitched.

 

-

 

The demon walked down still streets, the screaming of the boy finally going quiet.

When he threw him against the wall Muzan hoped the boy wasn’t dead, he did had a use for that one after all. Although hope was a rather strong word to use, he mused.

In the end everything went smoothly. He killed the mother with a flick of his wrist, took her form, and chose a child out of seven to turn into a demon.

A perfect plan, one so beautiful the carnage could be framed as a work of art.

He didn’t kill the other child either. The child with white hair was a marechi, their blood and flesh being incredibly intoxicating to demons as well as nutritious. It would give the other child a head start when he turned him into a demon.

After all he couldn’t remember the last time he’d made a demon on the outskirts of the city. He never came by it often, the streets being full of the poor and stray dogs, but he needed demons everywhere so he could find the blue spider lily. So, as much as he hated what most would call “the slums” it was a good place to demonize someone, better than the city at at least.

Plenty of poor scum to eat after all, he scoffed and continued on his way.

 

-

 

Sanemi's eyes snapped open and he gasped, his back and ribs were on fire and he could feel a jagged cut running along his face.

The blood had crusted over, and felt itchy on his skin. Every breath he took felt like something was stabbing his lungs. He wheezed and tried to push himself off the ground, dried blood slick on his skin.

Wait.

Why was he on the ground?

Sanemi coughed and a huge burst of pain shot through him.
He heaved in another breath and looked up at the rising sun, eyes wide and chest stuttering.

Sanemi didn’t know why but he was having trouble remembering what happened.
He gasped again and the more he breathed the harder it became to force air into his lungs.

Sanemi’s vision started getting black spots as he continued to gasp in air and he could hear someone yelling.
His gaze shifted to what looked like a woman running towards him and a man running in the opposite direction, his eyes landing on something just in front of him.

Sanemi’s eyes grew wet as once again, tears were all he could see, and he collapsed back to the ground, desperate to erase the dead eyes of his family from his mind.

His vision flickered and then the woman was holding him him in her arms, taking him somewhere. His vision went dark again and he coughed up something wet.

His mouth tasted like iron and he could feel what felt like blood drip down from his mouth.

Sanemi took in one more gasp of air before completely loosing consciousness, misery being all he’s ever known.

Notes:

Chapter has been edited plot wise, spelling will be fixed tomorrow because it’s 11:00 at night rn and I’m still processing what the heck I just wrote. Like wth is wrong with me 💀

because of new plot the next chapter may not make complete sense for like a few off comments, so… hopefully I get to that before anyone reads it.