The Tenth Pillar. (Kimetsu No Yaiba X OC)

Rivals

The Dimensional fortress trembled. All the demons and humans inside were taken back by the huge explosion.

It had such force that even the great Muzan was surprised by the impact.
Hiiro stood silent, little he knew about the strength of his moon fang.

The ground was cracked, the room was completely blown away, no trace of the beautiful japanes garden remained.
In front of the night pillar, an injured Douma layed.

He was already fading his life away. Even with his strongest demon art, he was defeated by the man in black.

The Reiastu blow cut half of his body, now he was just half of the demon he used to be. He had no strength left, not even to regenerate.

"Idiot. My Getsuga Tenshou was just the final blow. The reason you lost was not me, but the poison." Hiiro pointed his sword to his neck, slowly piercing it until the Upper Moon turned to ashes. "Never underestimate a Butterfly, scum."

Even if he was victorious, even if he avenged Kanae Kocho. Hiiro knew that the was far from over.

He ran a quick diagnosis of his body. He found nothing but small cuts and bruises, he was lucky, that ultimate ice technique was fearsome.

"Now le—" the pillar was interrupted by the ceiling being cracked open, a half dozen demons fell through it, he could see the despair  on his faces as they began to crawl away, trying to escape.

"YOU'RE NOT GOING ANYWHERE!" The boar masked boy barked as he pierced one of the demons back with his dual swords.

He performed his beast breathing techniques and in just an instant he finished with all the creepy crawling creatures.

"You have really grown, Inosuke." Hiiro smiled puffing his chest out.

"Sensei?! You're back!" The king of the mountain rushed to his master, more than a happy encounter, he aimed for a pig assault. "Fight me!"

Inosuke Hashibira met a bonk to his head, strong enough to stop his reckless charge. The tenth pillar was enjoying the reunion, he was glad that he remained the same even when he became much stronger.

"Imbecile. You're supposed to fight demons, not humans." Hiiro crossed his arms and sighed. "You have no remedy."

Both of them laughed without realizing about the presence of the pinknette, her green eyes gleamed as she silently danced through the room, like a tigress hunting her prey, Mitsuri Kanroji ambushed the night pillar, hugging him from behind.

"Hiiro-kun! You're back!" The young man felt 'them' squeeze against his back. He even swore that they were bigger than last time.

"Y-yeah." The raven haired boy reassured the love pillar. "I'm back, Mitsuri."

The time for reunions was no more. Hiiro had already a plan, tracking their Reiatsus, he figured the position of the demon slayers and the Upper Moons.

Tanjiro was fighting with Tomioka against Akaza, the third Upper Moon.

While Obanai was currently trying to slay the master of the fortress. Inosuke and Mitsuri are going to assist the snake pillar while the night pillar will assist Sanemi group.

"Shinobu, Kanao and Zenitsu are on their way to help Sanemi-kun and the others." He carved the positions of their objectives into the mud, the three of them were resting on the ground. "The girls have medical supplies for everyone. I'll catch up with them. Is there anything you want to say?"

Both, the love pillar and the boar boy shook their heads.

"Let's go, then."

Without losing any second, they all sprinted to their objectives.