Muzan

Yami flew across the night sky towards the explosion. He saw the pillars and Tanjiro attacking Muzan and he shot down from above, slashing down on Muzan's head. Muzan looked up and seethed "It's you!"

Yami didn't say anything but a giant Demon overlapped with Yami and slashed down with him.

Suddenly, Yami and everyone else fell into doors with Muzan going into a different door.

Yami fell into a door and looked at Muzan as he went, his eyes were blank with no hatred or anger, just blank. Muzan was startled by those eyes, they were looking at him as if to say 'I'm going to kill you because I want to kill you.' there wasn't a need for a reason, no need for anger or hatred.

Yami was going to kill Muzan because he wanted to kill Muzan. The fruit of his efforts all this time, the strength he trained for and wants, he will only be able to leave this world in peace if he killed Muzan himself.

He landed on the ground in a room and all the doors opened, demons flooded the room.

Yami swung his sword in a circle and beheaded all the demons in the room.

He looked at the ash flying around him and let out a purple breath as he said "Muzan... Wait for me." before blurring and flying into the hallways.

He blasted through demons like they were nothing, Yami's eyes were looking around as he listened to the evilest song he could hear. He cut through a wall and appeared in a room with bridges and water, he looked at Shinobu who was stabbing a demon through the neck on the ceiling. He flashed and caught her while she was falling.

He placed her on the ground and gave her a slap, waking her up. He poured healing potion down her throat and the demon appeared behind him saying "Excuse me, that's my pre-" his arms were separated from his body and Yami glanced at him.

The demon trembled for the first time in his life, feeling fear. He didn't notice that his fan was touching the scarf on Yami's neck. Yami dropped Shinobu on the ground and she coughed before chuckling. Yami stood up and the demon said "What are you laughing at?!"

Shinobu laughed and said "Idiot, don't you know? You died the moment you touched that scarf." Yami turned around and grabbed the hilt of his sword, the demon was stunned, this pressure... Even Muzan didn't make him feel this way!

Shinobu coughed and said "There's something you should know..." Yami flickered and appeared behind the demon, clicking his sword back into the sheath as Shinobu giggled "NEVER touch the Oni Pillar's scarf." the demon's head was severed from his body and falling to the ground, unable to comprehend what just happened to him.

Luckily, he didn't have to as his head had lines appear on it before it collapsed into cubes and turned to ashes. Yami looked at Shinobu and at the door before snapping his head in a direction and running away, leaving "Don't die, bitch." as he left.

Shinobu blanked and by the time she realized what he called her, Yami was gone. She had a belly full of anger but no outlet and Kanae ran in, checking Shinobu for injuries as she grumbled.

Yami cut through walls and continued through this maze of bullshit. He smashed through a wall and saw Giyu and Tanjiro, he threw healing and stamina potions at them before continuing on his way, through another wall.

He continued running through the maze of rooms, cutting down demons with a blank expression. He felt strange, his sword didn't feel like it was there. It felt like it was a part of his body. He cut down demons like vegetables and his song was singing loudly, the happiest song Yami had ever heard.

A while later

Yami slashed through a wall and came to a long hallway. He looked down at the vertical corridor and saw a mass of flesh. He simply jumped down and went headfirst holding the hilt of his sword and the sheath as he barreled down towards the flesh egg.

The egg opened and Muzan came out as Yami sped towards him like a bullet, Muzan looked up and Yami's hand blurred as he passed him. Muzan's head was separated from his neck and spun in the air, seeing Yami's emotionless eyes looking at him.

Yami slashed down and flew back up, landing on a platform and looking at Muzan's head with a blank gaze. Muzan's head flew back to his body and re-attached itself, he looked at Yami and said "Truly such a wonderful being you are... The perfect being that I've longed for. I originally thought you were a demon but you can survive in the sun! Not only that but you are physically stronger than any of the others... Your body... It has limitless potential!"

His gaze turned sinister as he said "I must have it!" Yami grabbed his hilt slowly but suddenly the maze like place they were in, exploded up onto the surface.

Yami was sent flying through the air along with Muzan, who was grinding his teeth in irritation. Yami kicked the air and flew towards Muzan, stomping on his chest and smashing him through the ground into several buildings on the surface.

Yami landed on the ground and walked towards Muzan, he slashed in front of him and the buildings in front of him were cut, sliding off their foundations and creating a path for Yami to walk on inhibited.

The rest of the Demon Slayers were on the surface as well and groaned in pain.

Yami walked towards Muzan, who got up and roared "DIE AND BECOME MY VESSEL!" as his arms stretched out and turned into sharp blades, slashing and spinning chaotically. Yami slashed up, sending a purple haze at Muzan that took the shape of an Oni breaking through the ground and grabbing at his ankles.

1st Form

Yami slashed back down as he continued his steps, a giant purple Kanabo slammed down on Muzan, who blocked with his arms. The other Demon Slayers and pillars started getting up off the ground.

2nd Form

Muzan charged at Yami thrusting his arm at him, Yami spun to the side and sliced horizontally, shooting a sickle that severed Muzan in half.

3rd Form

Yami stabbed through Muzan's torso with a thrust taking the shape of a spear. Muzan separated his body and connected by with his lower half before arms burst out of his back and swung around violently.

4th Form

Yami backed off and moved around quickly, listening to the song of warning coming from Muzan's limbs, while slashing and blocking the appendages. Muzan charged forwards and stomped on Yami's chest, sending him flying into a building.

5th Form

Yami spun in the air and landed on the building softly before jumping off and spinning in the air, slashing at the same time. The purple Haze covered him and made the shape of a stamp. (Enma is the King of Hell and in Japanese Folklore he has a stamp as a weapon or something like that. It might be called a 'seal'.)

Yami smashed through Muzan's arms and ran through his body, blasting his mid section to chunks.

6th Form

The chunks turned into spikes and stabbed at Yami, who started dancing around them blocking with his sword before jumping into the air and bringing his sword down on Muzan's head, with a purple lightning bolt coming with him, only to be blocked by dozens of hands as Muzan growled "You little rat, you're annoying me!"

7th Form

Muzan's back exploded into sword arms and the pillars, Tanjiro, Zenitsu, and Inosuke were trying to get close, slashing the chaotic sword arms. They were incredibly fast and the group were shocked at the fast that Yami was inside them right now, if they were fast outside here, how fast were they inside the area closest to Muzan?!

Yami held his sword out sideways in front of him and got knocked back, he pushed off an arm behind him and spun in the air as a purple wind covered him like a tornado, making Muzan gasp for air and claw at his neck. The arms in front of Yami were shredded to dust in front of the tornado and Muzan used his hand and punched out, blasting Yami away as Muzan hit his sword.

8th Form

Yami landed on the ground and ran at Muzan jumping to the side and rolling on the ground, dodging the arms, before jumping in the air as a giant purple Demon with a Kanabo appeared behind him, it overlapped with Yami's sword and smashed down on Muzan, who blocked with his arms, getting blasted into a building.

9th Form

Yami flipped in the air and landed on the ground, the rest of the pillars ran over and stood with him, having marks on their faces. Muzan came out of the rubble with solid red eyes and charged at the ground, creating the chaotic area again and flickering to Sanemi, stabbing at his gut before anyone could react.

Sanemi was stunned and thought he was dead, but a fiery purple circle cut Muzan's hand off and a kick sent him flying into an iron spiked ball, smashing his head to pieces as the rest of the attacks landed on his body and blew it to pieces.

10th Form

Muzan regenerated and swept his arms out in a fan in front of him, everyone jumped and dodged it but another one came where they were in the air. Tanjiro and Yami appeared in front of Muzan, crouched low as they drew their swords, slashing upwards, crossing blades and narrowly missing each other as two fans of purple haze and orange flames, severed the arms that were going to bifurcate the rest.

11th Form

Yami's horns were getting longer and glowing purple as he continued the entire style from start to finish. The other pillars took the opportunity and slashed at Muzan, cutting him everywhere as he blocked in front of him with more sword arms before swinging his arms out and roaring "ENOUGH!"

The air pressure made a few of the pillars fly back and they all blocked with their blades. Muzan's arms were wide open and Yami appeared in front of him, he slashed down a pentagon of purple haze before thrusting through it and piercing Muzan's head, cutting his upper half into 6 pieces shaping the pentagon in flesh.

12th Form

Muzan's head regenerated and Yami pushed off Muzan's chest, getting a spike through his foot as he jumped away. Tanjiro flashed in front of him and slashed at the falling arm sword, smashing it away from Yami, who grabbed Tanjiro and back flipped swinging Tanjiro around before throwing him at Muzan.

Tanjiro spun in the air and flames trailing from his blade as he cut Muzan in half diagonally, landing behind him before jumping away from the arm sword that was coming or his head. Yami lunged forward and rolled on the ground before sliding in between Muzan's legs and slashing his legs off sideways, then flipping his sword and slashing over his head, cutting Muzan in half vertically as he jumped off the ground to Tanjiro. This was Demon Gate.

13th Form

Muzan fell on his nubs and quickly regenerated but the attacks from the other pillars destroyed his body again. Yami sheathed his sword and held his arms out as Zenitsu and Inosuke jumped on them. Yami swung his arms forward and the two pushed off, shooting at Muzan.

Inosuke used his swords like scissors and cut Muzan in half while Zenitsu flashed and cut Muzan's legs, arms, and head off before grabbing Inosuke and backing away. Yami jumped in the air in place and Tanjiro sheathed his sword, lunging forward and rolling to his hands, placing his feet on Yami's feet and shooting him towards Muzan.

Yami traced a circle of purple flames then slashed 10 times making the 10 pointed star, blowing Muzan's torso into bits as he flew through him, the spun in the air and Shinobu caught him, getting held by Zenitsu, Inosuke, and Kanao.

14th Form

Yami's horns curled over his head and his eyes were solid purple, he stood up and held his sword in front of him, it burst into purple flames as he let out a purple breath of air. Muzan looked and the sun was starting to rise, before he could even think, Tanjiro and Yami appeared on his front and back. Yami and Tanjiro shouted "ONIS RULE THE EARTH/SUNFLOWER LANCE!"

The duo roared "Final Style!" Yami sliced down diagonally and Tanjiro thrusted through Muzan's lower half, pinning him to the ground as Yami flew over his head and rode Muzan's upper half. Yami spun his sword in his hands and held it above his head pointing down.

His and Muzan's gazes locked and Muzan truly felt fear, his eyes... They were the same as that man! Yami stabbed down, through Muzan's head and pinned it into the ground as the sun rose and covered the land.

Muzan started screaming in pain and his head opened vertically, intending to swallow Yami, but he took his sword out and pressed down on the back on the blade, keeping his mouth open as he pressed on Muzan's arms with his feet, getting cut up in various places, dodging the spikes from cutting his scarf.

Muzan started sizzling in the sun as his lower body turned to ashes and disappeared. Yami took back his sword and jumped off Muzan, slashing in every direction extremely fast, cutting the chasing Muzan to pieces and beating him back as he slowly turned to ashes and collapsed on the ground, looking up at the sky in a furious rage and was overwhelmed with grief and indignation.

Yami fell back down and pointed his sword down, stabbing Muzan right in the forehead as the head burnt to ashes and flew away, finally disappearing from this world.

Yami took his sword back, slashed the blood off and sheathed it before swaying and turning around. He took a step and fell flat on his face, he did it. He got help, but he did it.

He became strong.