The Tenth Pillar. (Kimetsu No Yaiba X OC)

Prologue

The last moon of the year arose in the clear sky. A new moon. A good omen, yes, a bad night for a villager to be drunk and lost in the forest and moreover if the woods are infested with creepy crawling creatures known as Demons.

Who could guess that this exact moment, the poor Koharu was drunk as hell and in a forest.

A nasty bloodlust was floating around, the air reeks of hunger. The poor Koharu doesn't even know yet, he's been observed, stalked, this demon likes it to be this way.

He likes to play with his food, to make them shiver and when they are terrified, he slaughters them and give a feast in their lifeless bodies.

"Hey, old fart. You shouldn't be walking in this forest, unless you have a death wish."

When the poor Koharu looked behind him, he saw him. A white haori male stood in the middle of the road, in his hands he held a sword, under his haori a black uniform, the old man knew what that means. A demon slayer.

"Mr. Demon slayer, what brings you here?"he asked as polite as his drunk ass permitted him. He knew the slayers are on a level of their own, and more reason if they are wearing a haori.

"Well, I got some rumors of some nasty demon in this forest" he walked slowly and without doing any sound. "And you should get out of here. Now!"

The poor Koharu didn't flinch, he ran away as soon as the haori male dictated.

When the villager got eaten by the darkness, the demon slayer spoke again.

"Your stench disgusts me. You really are a stinky one. Even me that do not possess that unique nose like the boy with the wooden box can smell you, miles away."

Nothing, the dark forest didn't respond. But, in that darkness, hidden at plain sight, a demon was trembling. He can't explain the situation, moments ago he was preparing himself for a feast, now every drop of demon blood in his body claimed to run away from there, like an instinct, a survival one. But, he was a proud demon, Muzan-sama himself conceded the demon art of stealth so he could prey on the weak. He was a demon, he realized that, he knew that there was no need to fear a punny human.

"You lowly human. You dare interrupt my hunt?" His deformed arm, fell like a lightning.

No normal human could evade it. In the blink of an eye, the demon slayer dissapeared. "What?"

"Hey, slow ass demon. I'm up here." The demon slayer was on top of a tree branch. Staring down at him pathetically.

The infuriated demon rocketed into a new attack, slashing in a frenzy, he didn't put any attention to whom he was hitting.

Like an easy training the white haori boy just evaded all te attacks, they were so slow that it was a boring fight.

'The Butterfly Estate training was harder than this.' A flashback crossed his mind, but there was no time to waste.

"Night Breathing. First Style: Night Slash" This was no more than a quick draw. A lightning fast attack with all his power, a dark plasma was left behind when he attacked.

The demon blood was shed, he realized his mistake. But now it was too late. The human has the upper hand. Without any doubt, he readied himself, no stinky demon shall escape.

"Night breathing. Second Style: Dusk Impact." With his unsheathed sword, a vertical slash stroke the demon, like the name implies, the Dusk Impact honors the time of the day when the night falls upon the skies, a falling impact.

The demon retreated again, a big wound ran from his shoulder to his waist, he got multiple organs, not the heart though, breathing was difficult, and his regeneration wasn't working properly.

"Who the hell are you, human?" He was trembling, he knew it was too late, he couldn't run away anymore. He was already dead. At least he has know the name of his killer.

"Why should I give my name to a stinky demon?" The grip on his sword got tighter, even veins were popping out of his hand. For the first time the demon caught a glimpse of the sword. A black sword, pitch black with a long chain attached to the handle.

"You like it?" The boy asked while he admired the katana. "It's name is Zangetsu. The slaying moon." A wide smile appeared in the slayer face. He was now pumped up, to kill a demon.

"I'll tell you something nice. Up till now, no weak  demon has seen more than three styles of my breath. But you, stinky. You are going to see the third style, be grateful."

The slayer took a deep breath. He felt the strength rising in every muscle in his body. The third style is one of the most powerful techniques of the night breath.

"Night Breathing. Third Style: La Luna." When he attacked, black plasma appeared again, like a dancing tide in the night. The third style was simple, yet powerful, a round cut, a total circular attack, like a wheel, no, the circular attack represents The Moon.

The demon didn't have time for anything else, his head was cut off, with a single slash. He was vanishing, slowly. He saw the demon slayer walking away, like if that fight never happened.

'Ah! He never told me his name.' The demon dissapeared without knowing the name of his slayer, at the end he became dust and got carried away by the wind.

When the poor Koharu saw the exit, the sunlight was already kissing the woods. The old villager never knew how good the sunlight could feel like, the gently warmth revitalized every cell of his old body. Hell, he feels like he's in his mid twenties.

He was close to his village, a twenty minutes walk and he'll see his wife again, he was alive, he was safe. Koharu eyes became teary.

"Hey. Mister." His eyes looked at the three young men standing in front of him, they wear the black uniform as well and carried a katana. "Did you came out of that forest?"

The old villager just nodded weakly, the demon slayer corps were everywhere, even to protect the meaningless life of a poor villager. It was then when poor Koharu came to his senses.

"The young man, t-the white haori man h-he's still there and..."

The sound of a branch being cracked stopped the old villager from his talking. One of the demon slayers unsheathed his sword.

"Identity yourself or else—" When they saw the white haori slayer, he bowed followed by the other two slayers. "S-sorry, we didn't knew that you were there, Hashira-sama."

Old Koharu saw clearly the man who saved his life. A raven haired boy, he was probably in his early twenties, no more than twenty two years, his eyes are golden and cold, but with a spark, a special spark that glows even when everything is lost. He was definitely tall, Koharu calculated that the boy was at least six feet tall, he wasn't thing but he was definitely not muscular, you can say he's athletic.

"Hey, old man. You're alive? I thought you'll get lost in the woods." The young man joked before walking past them. "You should go home, and never come back to this forest again."

He dissapeared, without any trace. Koharu didn't have a chance to even thank him. The only thing he saw was his back, the white haori had a number in his back.

"Mr. Demon Slayer. Who is that man?"
The demon slayer who bowed first gave a quick glance to the old man before answering.

"His name is Hiiro Kojima and like the number on his haori, he's the tenth pillar."