Demon Slayer: Kimetsu no Yaiba: Hinokami Flames

The Sun vs the Moon

Tanjiro continues to move through the everlasting changing fortress. He hears the screams of agonizing death as his comrades and demons die. 'I can't figure out which way's up or down. And there's so much going on! Kibutsuji's is somewhere and has Tamayo as his hostage, everyone's separated, and the fortress is altering around, making us suffer higher casualties! It's just like the demon from the abandoned mansion! But I already have the scent of him. If I can trace it, then I can find him easily!' 

In a bottomless shaft, Muzan still recovering from the sneak attack still holds Tamayo as her hostage. "Now that was indeed a foolish ploy, my dear Tamayo. Staying close to me as of now has guaranteed your death."

"And like I said before, I'll take it as atonement for my sins. I am more than ready to sacrifice my life to keep you from Tanjiro!"

"A sacrifice that will be in vain. So, I might as well deal with the resistance right in front of me." He proceeds to change his flesh but suddenly feels pain in his flesh manipulation. "Nngh! What was that?!"

"An effect from the drug. It'll keep you from using your abilities for some time. The next few hours you'll be unable to attack anyone. So, am I dying in vain?!"

"Lord Muzan."

"What is it Nakime?"

Nakime who is now the Upper Rank 4 was completely connected to the entire castle. "Tanjiro Kamado is has tracking you through your scent. It's only a matter of time until he finds you."

"Of all times!"

"It looks like the odds are against you, Muzan!"

"Don't be so certain. Nakime, why don't we keep him occupied?"

"Of course, Lord Muzan."

Then fighting through the pain, Muzan begins to form a flesh cocoon that also hold Tamayo. "What are you doing?!"

"Because of what you said, I'll stand no chance against him. So, I'll need to buy myself time. Which means, my Upper Ranks will act as the Hashira's opponents. And once this side effect is done, I'll emerge stronger than ever. But don't worry. You repent soon." The flesh surrounds Muzan and it starts to absorb Tamayo. 'No! He's forcefully creating a cocoon and is trying to counteract the drug that make him human! He's also plotting to absorb me! So, please... someone... help me!' 

'Tamayo's scent, it's gone!' Tanjiro realized. 'I won't let anyone else die! I'll stop you Muzan Kibutsuji!' Tanjiro blitzes through the cast killing any demons in his path. But as he keeps running, a wall compartment slams him through other walls. Recovering from the wall, he gets back on his feet, he finds himself in a new room filled with pillars.

"How many months has it been since our last encounter?" Tanjiro recognized that voice. "From what I've heard, you defeated, Gyutaro, and Hantengu. And you've unlocked your mark. You have become stronger from what I've seen before."

"I can even tell that you're different, Kokushibo." Tanjiro turns around seeing the powerful Upper Rank before him.

"It would seem as if you've become vitiable to Lord Muzan. You temporary became a demon. And you were able to withstand the sunlight."

'That's why he taunted me before.'

"I do have a mission. To bring you to him." He then unsheathes his sword. "But that doesn't mean you have to go... in one piece." Kokushibo then notices Tanjiro's mark. "Oh, I see. You now have shortened your life."

"What?"

"The scar on your forehead has altered into a mark."

Tanjiro then notices the same marks on Kokushibo. 'I wasn't fully aware of those marks on him until I unlocked mine. I honestly thought they were and effect or a family mark. But now I realize the heavy gap between us was extremely huge. But what did he mean by shortened my life?' He remembered back to when Yoriichi's soul spoke with him. "And when Muzan confronted my older brother, he lied and said that those who had the mark, would die at the age of 25."