The Tenth Pillar. (Kimetsu No Yaiba X OC)

Dimensional Fortress.

The Hashiras were rushing to the Ubuyashaki manor. They received an urgent message from the headquarters. Muzan was there, this was the chance to finish this conflict.

Sanemi and the other pillars were close to the mansion, they could already see it. The all felt relieved, just in time to save the master.

Suddenly a huge explosion blowed up the entire manor, so close yet so far, the Hashiras could only witness in shock. The master decided to blew himself and damage Muzan.

The father of all demons was astonished, Ubuyashaki was so calm, a serene smile plastered on his face before blowing himself and his family.

Kibutsuji Muzan was trying to regenerate and heal up, but a strange blood demon art was delaying his regeneration.

Suddenly, spike began to sprout from the ground, piercing and trapping the strongest demon. He knew he could just destroy them and escape.

"This is nothing!" But before he could move an inch, Tamayo appeared from nowhere, like a shadow and stabbed him. A medicine. "You bitch!"

"I've been waiting for this day, you fucker." The demon lady smiled with calm, even though she knew, she won't live another day. Tamayo felt her arm began to be absorbed by the original demon. "You will die, Muzan."

The father of all demons couldn't reply, Gyomei rushed and cut off his head, before the others came to him. Even Tanjiro Kamado was there, ready to fight.

"We did it..." Mitsuri whispered when she saw the headless body.

"DON'T LET YOUR GUARD DOWN!" The rock pillar yelled as he began to swing his axe again. "It's Muzan who we are facing, he won't die that easy!"

They saw in horror as the original demon began to grow a head again, he's without a doubt a monster. All the swordsmen prepared to strike with his breathing, from the wind to the water breathing, from the mist to the love breath. The will show no mercy to the demon.

Before they could get close to him, the space around him distorted. The slowly began to fall, they could see the angry demon looking down on them.

"I WILL KILL YOU ALL, DEMON SLAYERS, I WILL DEVOUR ALL OF THE UBUYASHAKI'S LEGACY AND PROCLAIM MYSELF THE WINNER."

The decisive battle against Muzan and his demons has begun. Now there's no time to waste nor to have a doubt.
The pillars were separated, they were in the secret fortress of the master of demons: The Dimensional Fortress.

Hiiro finished to suit up. The shinigami were kind enough to fix his tattered uniform form the demon slayer corps. Now is good as new.

"Yes, it's perfect." He proceeded to take his blade and sevired it to his hips. Everything was almost ready. "But this..."

The white haori didn't had the same luck as his uniform, it was dirty and ripped from his training.

"Awww man..." the night pillar on regret. But, no use on crying over spilled milk.

"Give me that." Soi Fon, captain of the second squadron, she snatched the old coat from his hands. "You will embarrass all the shinigami if you go with a tattered haori. Instead, take this."

Hiiro's eyes sparkled as he received the gift, he coul not believe his eyes. It was such a  perfect parting gift.

"Is it ok?" Before the girl could continue, the captain of the sixth squadron barged in.

"It's our gift, you should just wear it and shut up, kid." The cold swordsman spat.

"Byakuya-sensei is cold as ever..." the tenth pillar let his head fell, he then smiled and double checked, sword, bag, the special flask from Kurotsuchi-sensei and now this. "But I'm ready to go back..."