3rd POV. Infinity Castle.

After the conclusion of the battle against Upper Two, Doma.......

Sora, and the others took a break. They also began to discuss on how will they move from here on out.

Sora: We still can't navigate where Muzan is.

Sora: And the problem is that this fortress can literally shift dimensions over and over.

Kanae: Then, how are we going to locate him?

Sora: The crows have been doing that job.

Sora: But then, I guess it would be easier for us to find the demon that is responsible for controlling this castle.

Shinobu: You mean Muzan is not the one controlling this castle?

Sora: No. Muzan would be too busy recovering.

Sora: So......I believe our next priority should be the demon responsible in controlling this castle.

Sora: So, here's the plan.....

Sora: I'll locate the demon and then force that demon to dispel the castle and drag Muzan out of the open.

Sora: For now, Kanae, Shinobu. Go and find other demon slayers and support them.

Sora: We'll definitely need as much help as we can get. I'll also try the same.

Kanae: Will you be fine on your own?

Sora: Don't worry, I've survived so many times on my own.

Sora: I won't die that easily.

Kanae: .........

Sora: Now then.......

Sora decided to part ways with the group and continued on to navigate the castle.

Sora: Damn, this fortress is changing layouts constantly.

Sora: We're just lucky that the crows are still able to guide us.

He felt like he is navigating a long hallway, one without end.

Sora: As long as we're still inside the enemy's territory, we won't be able to drive Muzan into a corner.

Sora: I know I can just kill him but knowing how Amaterasu works, the Sharingan, the Breath of the Sun.......

Sora: All I have to do is to find his weakness.

Sora: The Sun is the only remaining method to kill, right? He resisted death by decapitation......

Sora: We don't even know how much time has passed since we all fell here.

Sora: Still, with two Upper Rank demons already dead......

Sora: Upper One is still a mystery to me. I haven't met him.

Sora: Kagami, who's the one fighting Upper One?

Kagami: Gyomei, Sanemi, Muichiro, and Genya.

Sora: I guess with Gyomei-san there, everything will be fine. I'm sure they will tell me to focus in locating Muzan.

Kagami: That is your orders. Go straight to Muzan.

Sora: All right.

Sora: What about Giyuu, Kyojuro, and Tanjiro?

Kagami: They are also finding a way towards Muzan.

Sora: The more area we cover, the more chances we'll find him. But we don't have much time.

Sora: Tamayo-san can't even endure much longer pinning Muzan down.

Sora: We have to hurry.

Sora: But the only way to reach Muzan quickly is to drag him out of this damn place and then prolong the battle until the Sun is out.

Kagami: You maybe right. Fighting him inside of here would be useless.

Sora: And that is the reason why I have to locate the demon who is controlling this fortress.

Sora followed Kagami to navigate throughout the castle and when Sora heard noises from his left side.

He opened another door and saw that it's like the central section of the castle and it's constantly changing.

Sora: What the......

???: Kyaaaaa!

Sora looks for the source of the scream he just heard and finally, he saw none other than Mitsuri who is dodging and cutting the doors and building sections with her blade.

Sora: Mitsuri. Right, if I can find any other allies along the way!

Another building crashed and it destroyed Mitsuri's foothold and she's falling now.

Mitsuri: KYAAAAAAAAAA!

Sora: Oh shit!

Sora jumps down, dons the Perfect Susanoo Armor, and flew towards her at top speed to save her.

Mitsuri closed her eyes as she knows she'll be dead or so she thinks.

When she opened her eyes......she saw that Sora is carrying her and they went to a place with a proper foothold.

Mitsuri: Sora-san!

Sora: That was close.

Mitsuri: He's wearing a cool armor with wings. Like a tengu!

Sora: So......what the hell is going on here?

Mitsuri: Right! Over there!

Mitsuri points towards the direction where a woman with a biwa is sitting, the new Upper Four, Nakime.

Sora: So that's the demon controlling this castle.......and not to mention, she's the new Upper Four.

Mitsuri: We don't know how are we going to get close to her.

Sora: We?

Mitsuri: Iguro-san and I are the ones fighting her!

Sora observes the place and saw a figure wearing a striped haori evading Nakime's attacks.

Sora: Alright, stay here for a while. We got to regroup.

Sora flies towards Obanai and saved him from another incoming attack.

Obanai: What!?

Sora: I'll answer your questions later!

Sora grabbed Iguro with the Susanoo's skeletal hand and brought him to the place where Mitsuri is.

Obanai: Kanroji! Are you okay!?

Mitsuri: Yeah! Sora-san saved me.

Sora: All right......let's see.......

Sora observes the surroundings........

Sora: Iguro, Mitsuri, have you two been fighting Upper Four since the beginning?

Iguro: Yeah.

Iguro: The biwa demon's blood demon art is not really lethal but she's stalling us. I'm surprised you even reached this place.

Sora: I'm actually planning to kill the demon who is controlling the castle in order to drag Muzan out.

Mitsuri: So, you believe that if we get the biwa demon, we'll be able to reach Muzan?

Sora: Yes, and it will turn the tide into your favor.

Sora: It's dangerous to fight the enemy in their territory.

Sora: And our plan is to drag him out and burn him under the Sun.

Sora: But the light of the Sun won't be able to reach this fortress.

Iguro: I see. So you shifted targets.......

Sora: Yes. Like in the game of shogi. In order to get to the king, the best way to do that is to capture all the king's subordinates first.

Sora: For now, we already defeated Upper Two and Three.

Sora: Gyomei-san, Shinazugawa, Muichiro and Genya are the ones fighting Upper One.

Sora: And then, we have the biwa demon, the new Upper Four.

Iguro: Do you have any plans to get close to her?

Mitsuri: Oh! Sora-san! Do the thing were you are being transported into a certain place in an instant?

Sora: You mean Amatsumikaboshi? I can do that but my range is limited, only around 10 meters.

Sora: And it should be within my line of sight.

Sora: If she blocks my field of vision, it would be useless.

Iguro: And she constantly changes the orientation and the places of each building.

Sora: So yeah. It would be difficult even for me.

Sora: So, if the demon is able to control the nature of the place......

Sora: Hmmm........

Sora: After all, as of now, she's the one with the advantage.

Mitsuri: Then what do we do!?

Sora: ........

Sora: Is there even a single one........?

Obanai: Huh? What are you talking about?

Sora: A blindspot.

Obanai: A blindspot?

Sora: There must be because look!

Sora points at Nakime.

Sora: She can't even turn her head from left to right, it's bound by some roots or something.

Sora: So, if we can get behind her, and then I'll force her to dispel this fortress with my Sharingan.

Obanai: Sounds like a plan.

Sora: We got to move and we have to cover more ground so better if we split up.

Sora: Don't worry about falling, I won't let you guys fall to your deaths.

And now......

With Sora's arrival, Mitsuri and Obanai's chances of getting Nakime have increased.

They split up and began moving to get to Nakime.

With constantly shifting buildings, doors flying towards them......

The three of them are now stalled in a battle, but Sora described it as like chasing a mouse.

Sora: There is no end to this! We'll be forced to be stalled here until one of us gets crushed......

Sora: Wait, can I just control her via Kotoamatasukami? Over a long distance? Well, I did that before......

Sora: But if she continues to disrupt my focus by messing our surroundings, it's no use

Sora: We got to find out how to stop the Biwa Demon.

Sora: Even if I use the Perfect Susanoo's armor and fly, the columns and doors will just constantly get in my way.

Sora: We have to sneak in, the blindspot that I've been looking for.......

Sora: Iguro and Mitsuri won't last long as they will run out of stamina. That also includes me in a sense.

Sora: Where is it.......?

But the battle dragged on for too long but they received the news of Upper One's defeat, however......

Kagami: Genya and Muichiro died in the battle.

Sora: ........

Sora: Damn it. Maybe I should've assisted them as well but......

Sora: Muzan is still our top priority.

Sora: And with only one Upper Moon remaining.......

Kagami: I received news! Muzan has revived! The Hashira needs to gather!

Sora: Shit!

Mitsuri: What!?

Obanai: Damn it! Even with Sora's help, this is difficult. He can't even focus and use his abilities as the Biwa Demon will disrupt his focus.

Kagami: The Hashira needs to gather now.

Sora: What!?

Mitsuri: Are you saying we have to leave the Biwa Demon?

Sora: But if we don't take her out, we won't be able to drag Muzan out of this place!

As Mitsuri and Sora regrouped.....

Both of them were pulled on their haoris dragged upwards by none other than Yushiro.

Sora: Yushiro!

Yushiro: I'm glad that you're still alive, Sora.

Sora: Hey.

Sora: Anyways.......what are you doing here? Do you have some sort of a plan?

Yushiro: Yes.

Yushiro: Remember my blood demon art that allows me to become invisible?

Sora: Oh, yeah, right.

Mitsuri: He's a demon!?

Sora: Don't worry, he's on our side.

Sora: Anyways, Yushiro, are you thinking what I'm thinking?

Yushiro: Yes. I guess with your help, I may be able to do that so easily.

Sora: Hmmmmm, let's follow this plan.

Sora: Mitsuri, Iguro, and I will continue to run around. Yushiro, sneak upon Upper Four's back and seize control of her mind.

Sora: Once you've done that, I'll strengthen the mind disruption with the Sharingan and if possible, if I can remove Muzan's control on her via the Kotoamatsukami.

Yushiro: That's a good idea! Wait, why didn't you used that earlier!?

Sora: If I use that, then my physical body would be vulnerable. You know that I have to enter the mind of my target!

Yushiro: Right......I forgot.

Sora: So......sound's like a plan?

Yushiro: Yeah.

Sora: Alright. I'll create a significant diversion and control Muzan.

Sora: Also............Tamayo-san.........

Yushiro: That is the reason why I'm here. I'll drag Muzan out.

Yushiro's hatred is clear as veins begin to pop out.

Yushiro: I'll make him pay for committing the greatest crime in the world.

And so, with that in mind.......

They began to move.

When Sora found a stable foothold, he activated his Eternal Mangekyo Sharingan, and his Susanoo on the skeletal stage.

Sora: All right, this will do!

Sora: Yasaka no Magatama!

The Susanoo throws three magatamas towards Nakime but the biwa demon saw this and used a column to block the attack, but it lead into an explosion that caused to form a large cloud of smoke.

Sora: Yushiro, I hope you made it in time..........

Sora rushed towards the location of Nakime and when the smoke cleared........

Yushiro finally succeeded by hijacking Nakime's vision and senses by putting one of his paper tags on the demon's eye.

Once Yushiro began hijacking Nakime's senses, the entire fortress begins to shake violently.

Sora: Oh shit! Even if we don't cut her head......!

Mitsuri: KYAAAAA! HEEEEELLLLLLP!

Iguro: KANROJI!

Sora noticed that Mitsuri is now falling to her death once more, while Iguro is struggling with his footing from the crumbling fortress.

Yushiro: Don't worry about me, Sora! This is my fight! Go save them!

Sora: Got it!

Sora dons the Perfect Susanoo's armor once more and flew towards Mitsuri to save her once more.

Mitsuri: Ah, the tengu has arrived!

Sora: Right......

Sora: Oh.....

They noticed that the space is beginning to shift drastically........

Sora: Alrigh, I have to do this now.

Sora: Susanoo!

This time, Sora used the Perfect Susanoo but he still modified the size.

Sora used it to save Iguro as well. Now, as for the Perfect Susanoo, the user is inside a hexagonal gem and can even allow access to whom he choose to enter.

Iguro: Woah, so this is what Kanroji was talking about.

Mitsuri: This is the first time I saw this form. It is really like a tengu warrior from the legends!

Sora: This is the Perfect Susanoo.

Sora: Mitsuri, the ones you saw back then at the Swordsmith Village, those are still like the development stages.

Sora: But when I got to master the Eternal Mangekyo Sharingan......

Sora: I was able to manifest the Perfect Susanoo.

Sora: It's a battle of wills between Muzan and Yushiro.

Sora: The castle is crumbling, the buildings and the overall surroundings are shifting in a violent frequency!

Sora noticed that the a column is coming upwards towards them and he decided to use the armored Susanoo for a while.

The column is going upward in a violent speed.......

Iguro: Even though I'm inside of this thing the pressure is too strong!

Sora: Hold on! Brace yourselves!

Yushiro and Muzan battled for dominance.......but then Muzan...

Who is facing Tanjiro, Kyojuro, and Giyuu......

When Muzan saw what is happening.......he clenched his fist.....

And at the same time, killed Nakime.

Which then result the Infinity Castle crashing down or upwards as the buildings are currently going upwards.

With the castle crashed.........

All of the Upper Rank Demons are dead........

For those who are under the Susanoo's protection......

They are practically unscathed, but what welcomed them is a total mess of debris......

And they can see a city in view.....

Sora: Oh no......

Iguro: The city.......

Mitsuri: This is bad! The civilians will be caught up in the fight!

Sora: Shit! We got to hurry now!