Speedrunning the Infinity Castle

"We found the location of the Infinity Castle. It exists in a separate dimension, outside the time and space of this world."

"Nakime's ability connects to that dimensional fortress... The high-ranking demons now called the Upper Ranks are stationed in the Infinity Castle."

"Sora, you can't kill this guy, or Nakime will die too."

Shisui worked quickly. Not only had he figured out that this wasn't the Shinobi World, he had also seen in Muzan's memories Uchiha Sora's previous arrival.

Though Shisui badly wanted to kill this demon who had caused countless tragedies, he knew Sora wanted the Infinity Castle, so he made that clear beforehand.

"Mm... I know."

"Let's control him first and have Nakime open the Infinity Castle. We can check out the merchandise."

Uchiha Sora glanced back at the Demon Slayer Corps members and said coolly, "Don't do anything unnecessary. Just stand there and watch."

Buzz—

The sound of a biwa string rang out, and a square opening appeared beneath Uchiha Sora and Shisui.

Uchiha Sora grabbed Muzan by the hair, and the three of them fell through together.

"Ah... There are quite a few of those things. Let's start recruiting the weaker ones."

Back in the Shinobi World, Uchiha Sora had already decided how to use some of the demons in the Infinity Castle.

He intended to take every demon with him, Muzan included.

It wasn't that he expected these demons to be of much use to him.

Compared to his and Shisui's ocular prowess, Muzan had been utterly helpless, but he was still about as strong as a Special Jōnin.

And then there were the demons like the string-wielders, whom he remembered as being roughly Chunin-level...

Demons that couldn't be killed were perfect for training the Uchiha youngsters.

He could set up challenges for them to gain experience, and once they reached a certain level, they could go out and take on missions. It would be just like a training camp for beginners.

The Infinity Castle could also serve as a safeguard for all the Uchiha.

Unless they were killed instantly or something similar, they could escape into the Infinity Castle and stay alive. It was like everyone having the Reverse Summoning Technique on hand at all times.

The stronger Uchiha could also learn Izanagi, giving themselves multiple layers of protection.

Uchiha Sora believed in protecting clan members who didn't want to fight and doing his best to keep those who did want to fight from dying needlessly.

--

Kaigaku Inadome, the new Upper Rank Six.

He had once been a swordsman in the Demon Slayer Corps, but after encountering Upper Rank One, Kokushibo, on a mission, he had turned into a demon to survive.

His evil nature wasn't born of a desire to survive. Even as a child, he had put out an incense burner that could repel demons, drawing them in to kill his companions.

A demon's instincts told him that the man being dragged along like a dead dog was the root of all demons—the Demon King, Kibutsuji Muzan!

Without the slightest hesitation, he dropped his sword and fell to his knees, begging for mercy.

"My lords, I am..."

Swish—

A scorching blade of light cleaved him in two, and he turned to ash in an instant.

"This one won't do. He's too weak."

Uchiha Sora gave his assessment in a detached voice.

Compared to an ordinary demon, this Upper Rank was a little stronger, but he was nowhere near good enough to be a mini-boss for the training challenges.

Nakime didn't need an interview. She was already a hire on the shortlist.

Uchiha Sora had made this trip entirely because of her.

Using Muzan as a converter, Shisui ordered Nakime to teleport Upper Rank Three here.

Like the demon before him, Akaza saw Muzan right away.

Though deeply shaken, he didn't make a fool of himself like the previous one had.

He took up a fighting stance.

"So this is it... Wonderful..."

"I can tell just by looking at you how powerful you are. If you kill me, that wouldn't be a bad end at all!"

Uchiha Sora slowly raised his hand.

"Sorry, I can't grant your wish."

"I've got a great job lined up for you—no days off, all year round."

Boom!!!

Tangible chakra crushed Akaza flat against the ground!

Chakra: Pressure.

After testing this way of using chakra on Uchiha Itachi, Uchiha Sora had fallen in love with the feeling.

Shisui glanced at him and inwardly clicked his tongue.

It would save chakra to use a jutsu, but this kind of waste...

Still, it looked so cool. It was great to have lots of chakra.

I need to train harder too...

"Next."

Doma, Upper Rank Two.

His rainbow-colored irises and immaculate, white-oak-colored hair made him look exceptionally elegant and beautiful.

He didn't experience the joys or sorrows of an ordinary person, and he didn't know fear.

Even after seeing Muzan's miserable state, he simply covered his face with a fan and laughed.

"Ohoho, I've never seen such powerful people before. Did you take down the great Lord Muzan~?"

He glanced at Akaza, pinned down by the chakra, and his smile widened. "How unusually sensible of you, Lord Akaza."

Turning to Uchiha Sora, Doma chuckled. "I can submit, too. I don't mind doing anything."

"Because... you're beautiful~"

"Like a scarlet spider lily growing on a volcano, beautiful enough to tempt people into walking to their deaths."

"I'm moved that I can continue working with Lord Akaza—"

His voice abruptly cut off.

Watching the flames rise over his body, Doma asked with mild confusion, "Why? Shouldn't I be stronger than Lord Akaza?"

"Ah, I just can't stand the way you talk. That's all."

"I... don't quite understand."

"You don't need to."

Uchiha Sora formed a hand seal with one hand, and scorching flames consumed Doma, leaving only ash behind.

Akaza, who had been resisting with all his might, relaxed a little.

"Next."

Upper Rank One, Kokushibo.

His original name was Tsugikuni Iwakatsu. He was the elder brother of Tsugikuni Yoriichi, who had dealt Muzan a devastating blow.

Jealous of his younger brother's talent and afraid of the Curse that doomed swordsmen with the mark to die at twenty-five, he had chosen to join the demons.

Muzan valued him immensely. He didn't treat him as a subordinate to be ordered around, but as something closer to a partner.

His strength could be considered equal to that of all the other Upper Ranks combined!

Clang!

Being captured alongside Muzan didn't break his fighting spirit. The moment he saw Uchiha Sora and Shisui, he drew his sword.

"Can't you recognize the difference in strength?" Uchiha Sora said coolly.

Kokushibo gripped his sword in both hands and replied in a low, steady voice, "In the presence of one as powerful as you, it would be discourteous not to draw my sword."

Uchiha Sora's eyes lit up.

He drew Ryuzuki. Deep crimson patterns shimmered across its blade, giving it a magnificent appearance.

All six of Kokushibo's eyes trembled.

Once Uchiha Sora had drawn his sword, Kokushibo could clearly see the shadow of that man...

As scorching as the sun, a presence he could never reach!

--

--

He hadn't even seen the sword's path.

He didn't feel the wound until several seconds after he had been cut.

Clang—

Uchiha Sora sheathed his sword and spoke calmly from behind Kokushibo. "Unlike that useless Muzan, at least you still have the desire to improve."

"I'll take you to a new world. If you prove yourself, you may yet reach an even higher level."

Rip—

Blood sprayed as the sword forged from Kokushibo's flesh fell in two pieces into the pool of blood.

"From today on, I am your master."