Bloody Sun, White Moon
(KnY Role Swap Fic)

Kibutsuji Muzan stares at the carnage before him. Numb. His brain is having a hard time processing what he just experienced.

Muzan likes to call himself a normal person. Well, sure he sometimes is pretty nasty and sadistic, but it was not his fault. If his idiot of subordinates can't even do simple mathematics or smooth-talking persuading customers, then they are deserved tongue lashing. And he has really strange health conditions where his heart likes to going still for a few short moments before resume beating, causing him prone to having a sudden seizure. But aside from that, Muzan can't think anything that warranted a massacre.

Certainly not from a monster coming straight out from fairy tale. A very hideous monster with rotting stench of sewage left uncleaned for months. A monster that looks like a sickly corpse with bloodshot eyes with black sclera, gaping mouth with sharp teeth across its torso and its lower body covered in grayish fur and has horse legs replace its actual legs. From its back was a tentacle-like appendage.

The noise and screams sent Muzan awake (a downside of living above your shop). He initially thinks it was a burglar or someone play a prank and prepared to give them a piece of his mind. Only for the words die on his throat when facing with a hideous monster. One that clearly is an abomination.

Stunned, Muzan took a step backward, which knocked a table, and Muzan was very sure his heart briefly gave up on him (again) when the monster turned. He nearly vomited when he saw the monster was in the middle of chewing a human's hand.

"hOOmaaaNNnn..." growled the monster. It sniffed and Muzan feels an unholy shiver go down his spine when it smirked. "MaaAAArrreeechiii...!" and it lunged at him.

Muzan definitely did NOT scream like a little girl as he made quick dodge. Barely missed the appendages from hell, he turned around and run. Using whatever left of furniture and the dead body to give himself a chance to survive. To live.

It was pure bad luck he tripped over a marble of all things, which forced him to stagger lest he fell face first. But that's all the monster need for it to wrap its tentacle around Muzan's ankle and lift him into the air, closer to the monster's unnaturally wide mouth and sharp bloodied fangs.

Muzan feels dread pooling in his stomach at his impending death.

Then salvation comes like a blessing from heaven.

"Breath of the Moon, Eight Form: Moon-Dragon Ringtail."

A single, gigantic slash slices the Tentacle in a neat cut. Dropping Muzan who barely manages to avoid a broken neck. His red eyes widen in surprise as someone jumped through the hole in the wall and landed between him and the monster. A swordsman with purple and black haori over the black uniform.

"First Form: Dark Moon – Evening Palace."

With a swing of the sword, that spawned crescent-moon like afterimages, the swordsman beheaded the monster, which let out a dying last roar before it vanished into black smoke.

Muzan collapse on his knees. His mind is still reeling, 'what the fuck just happens?'

He notices that the swordsman was staring at him.

"What... what was that?" Oh, how Muzan hates how weak he sounds. "That thing... is a crime against nature."

"Demon." The swordsman replied matter-of-factly. "Man-eating Demon. Bane of humanity everywhere."

Man-eating Demon? Aren't those supposed to be a myth?

"Myth had to come from somewhere." Did Muzan said it out loud?! "And this one, come from true story, as you had witnessed. Demon eats humans. For them, we are nothing more than cattle to slaughter. Although..." The swordsman eyeing the remnants of Demon. "They usually hit place out of the way or when there are few people. It was very unusual, or perhaps dumb, for this demon to attack a shop this close to civilization. Hmm... what prompts it, I wonder?"

"...it calls me... a Marechi, I think?"

"Ah. No wonder." The swordsman nodded. "A Marechi is a delicacy to Demon. That makes sense, yes."

Muzan finally got his trembles under control. Shakily, he stood up. "Who are you? How... how did you know so much about this Demon stuff?"

"I am a Demon Slayer." The Swordsman introduced himself with a courteous bow. Not too deep to show sign of submission, but low enough to be respectful.

"Demon Slayer?"

"Aaa. If Demon exists, a Slayer have to kill it to protect other humans. Basically, they are pest and we are pest exterminator. It is my job to find a demon and kill it, no matter what happened. Otherwise, life will be lost."

'Like my staff.' Thought Muzan, eyeing the torn up bodies and pool of red blood. 'Like what almost happens to me'.

"You should get somewhere safe. You don't want to explain to pesky polices why this place is like this, do you?"

"Hey... wait!" Did the Slayer plan to go just like that? "Where are you going?"

"Somewhere. Anywhere. Finding Demon." Was the nonchalant reply. "My job here is done. I don't see why I should stay."

Such a heartless answer! Is all Slayer this heartless?!

"How about me?" He asks. "This Marechi stuff attracts them, doesn't it?"

"...yes?"

Muzan feels his eye twitched. This Slayer... he isn't right in the head. "What if a Demon attacks when you're away? That means you failed, don't you?"

Oh. Now the Slayer's vacant look in his eyes disappeared. Muzan had to stop himself from flinching at the cutting gaze.

"What do you want?"

"Train me." Based on the surprised look, certainly, the Slayer didn't expect that. "I refuse to be weak. I refuse to be cattle. I refuse to be helpless again. I'm not going to sitting duck and praying for salvation if I can earn it with my own hands."

The Slayer gave him a hard look. "I don't have time to play babysitter."

"Then direct me to someone who has time." Insisted Muzan with an arm fold. "Surely some Slayer out there is willing." Maybe the old geezer who's looking for a successor. That kind of old geezer always exists. Human entrusted their hope and ambition and dream from generation to generation. Otherwise, how could they advance this much from cave dwellers they're once was? "I don't care who is it. I don't care how far they are or if I had to walk all way there. I'm not going to stop bugging you until I get what I want."

A blade touched his neck.

"Be careful of what you say." Whispered the Slayer. "Had I was a Samurai, I will take your head as the price of your arrogance."

"But you are not, and if you kill me you are no better than Demons you hunt, don't you?"

The blade pressed against his neck, drawing some blood before the Slayer sheathes back his sword.

"Paradise Cult." He said. "Go to Paradise Cult, five towns at North. Find a man named Douma. He will be your instructor." And just like that, the Slayer was gone. Leaping into the night and never looked back.

Muzan grumbled. "What a rude bastard. Not even bother to introduce himself."

Still. At least he has a goal now. To become strong so he won't be helpless anymore. The first step, find a man named Douma in Paradise Cult (like, really? A Cult?) five towns down south.

His heart disease might be a major setback, but damn it! He refuses to be cattle! He is not prey! And his heart would always beat again after a few short moments of stillness. Most of the time he won't even notice it so it's fine. His defective heart is not enough reason to pursue power. Purely for self-defense, of course.

With that in mind, Muzan went upstairs to packed his stuff. Some spare clothes, a few food and water for the journey, money, and some knives. Just in case he had to fight. Demons at night, bandits and thief at day.

When he slipped out via backdoor, he heard that the neighbor finally, finally¸ take notice of the strangeness and investigate. Muzan had no desire to answer questions, so he runs.

To the future. To the place where he will be strong. To change his fate.

TBC

a/n: a KnY Role-swap.