The news of the defeat of Upper Moon Rank Two spread across the entire battlefield through the cries of the Kasugai crows.
Shinobu, Kanao, Inosuke, Zenitsu, and Alpha, these five had defeated an Upper Rank demon.
The announcement sent a surge of motivation through every Demon Slayer who heard it. An Upper Moon had fallen. They were one step closer to victory.
Somewhere within the headquarters, the Ubuyashiki children, all five of them, sat gathered around a table. Talismans rested upon their foreheads as they continuously drew and redrew the layouts of the ever-expanding Infinity Castle. Their hands moved quickly, carefully mapping the shifting structure.
They, too, were smiling.
Upper Moon Two had finally been defeated.
Akira, who was speeding through the Infinity Castle while dragging Yushiro along, also heard the news through his Kasugai crow, Raven.
"Are there any casualties?" Akira asked immediately.
Raven answered, "No. Everyone survived."
Akira let out a quiet sigh of relief. "That's good."
Without slowing down, he accelerated even more.
Behind him, Yushiro, still being dragged at high speed, could only scream in protest as the scenery blurred past.
Erika, who was flying through the Infinity Castle, also heard the announcement from her Kasugai crow, Rose.
She smiled faintly. "That's good."
Then she asked, "Where should we go now?"
Rose replied, "There is a powerful demon presence near us. It is stronger than even Upper Moon Two."
Erika's expression sharpened. "Is it Muzan?"
"No," Rose answered. "It's different."
Erika exhaled softly. "Then I guess it's Upper Moon One…"
She sighed. Akira had wanted to fight him himself. But since she was here, she might as well face him.
"Be careful, Erika-chan", Selena's voice echoed telepathically. "Upper Moon One is strong. Far stronger than you think."
Erika asked back, "Can I beat him?"
There was a brief pause before Selena answered, "I don't think the current you can beat him."
Erika let out another sigh. "Then what should I do?"
"Try fighting him. There are a few Hashira near your location", Selena said. "All you need to do is buy time. But be careful, he's dangerous. Don't let your guard down."
Erika nodded to herself. "Okay."
With that, she changed direction midair and flew straight toward the signal.
On the other side of the Infinity Castle, Akira finally found what he had been looking for.
The new Upper Moon Four—Nakime.
She was a pale woman wearing a black kimono, sitting quietly while holding a biwa in her hands. A single, massive eyeball, like that of a cyclops, dominated her face. The eye was pink in color, with the mark Four etched clearly into it. Her hair extended backward, merging into the wall behind her, spreading outward like tree roots embedded into the castle itself.
From behind a nearby pillar, Yushiro peeked out while watching Nakime together with Akira.
"I thought Upper Moon Four was already dead," Yushiro whispered.
Akira replied quietly, "Maybe that spot was already replaced."
Yushiro frowned. "Does that mean there's another Upper Moon Three, too?"
"Probably not," Akira answered. "I don't think Muzan has many demons on that level. She's likely only Upper Moon Four because she isn't as strong as Akaza."
Yushiro hesitated. "Are you sure?"
Akira narrowed his eyes slightly. "Anything can happen. But for now, we can be sure of one thing."
He looked directly at Nakime.
"She's controlling this dimension."
Akira's Mystic Eyes could clearly see it; the energy signature surrounding Nakime was deeply intertwined with the Infinity Castle itself. The flow, structure, and spatial distortion all originated from her.
There was no doubt about it.
Akira turned back to Yushiro and said quietly, "Then, just as we planned. Are you ready?"
Yushiro nodded, his expression serious. "Please don't accidentally kill her. If that happens, everything will go wrong."
With that warning, he walked away, disappearing into the shifting corridors.
Akira sighed. "What does he think I am?"
Still wearing his armor, he walked calmly forward and stepped onto a platform high above. He looked down at Nakime without saying a word.
Nakime slowly turned her head, her single eye locking onto him.
Akira smiled faintly. "Sister, play that song."
"Sure, I got you," Selena replied telepathically.
Then, a new song began to play.
[No Difference from Aldnoah Zero]
The moment the music started, Akira jumped from the platform, rushing straight toward Nakime.
Nakime plucked a string on her biwa.
A massive pillar made of stacked rooms erupted upward in Akira's path.
Midair, Akira tried to punch through it.
Before his fist could land, Nakime plucked another string.
An open tatami door appeared directly in front of him.
Akira instantly recognized it, a portal door.
"Bad idea to go in there," he thought.
But suspended in midair, gravity would eventually pull him straight into it.
Akira punched the air in front of the door.
A shockwave exploded outward, similar to Akaza's punches, and the force blasted Akira backward. He was forced to retreat slightly.
Just as he was about to land.
Another tatami door opened beneath him.
This time, he would definitely fall into it.
Instead, Akira kicked the air.
As if stepping on solid ground, his foot connected with an invisible surface. He propelled himself forward, landing cleanly on a normal floor.
Even Nakime showed a slight reaction.
She was surprised.
Yes, Akira had just performed a midair jump.
It was the same technique he had used before, back when he caught Erika while she was falling. By kicking with enough force, he generated shockwaves, essentially using Akaza's principles, creating pressure solid enough to step on. It allowed him to walk on air.
It was similar to Rokushiki Moonwalk, though far less refined.
Akira steadied himself for a brief moment, then launched forward again toward Nakime.
Nakime plucked multiple strings on her biwa.
Instantly, several pillars made of stacked rooms grew out of the floor and walls, slamming toward Akira again and again.
Akira did his best to dodge.
He couldn't afford to take a direct hit, not because he couldn't survive it. With his armor, he was confident he could tank the impact easily. The real danger was the tatami portal doors mixed into the attacks.
Falling into one of those would be disastrous.
Akira dodged desperately, but wherever he landed, new tatami portal doors opened beneath his feet. Each time, he escaped by using another midair jump, kicking off invisible shockwaves to avoid being swallowed.
Nakime's attacks continued relentlessly.
Akira kept dodging.
It became a stalemate.
"Tch," Akira muttered. "Well, if getting close doesn't work, let's see if long-range attacks do."
He jumped back and punched the air in front of him.
"Destructive Death: Air Type."
Shockwaves tore through the space ahead, racing toward Nakime. It was the same technique he had stolen from Akaza.
Nakime responded instantly, summoning more pillars of rooms to block the attack.
The rooms shattered under the impact, but Nakime herself remained unharmed.
Akira launched more shockwave attacks.
Nakime blocked every single one the same way, retaliating with even more pillars crashing toward him.
Once again, the battle returned to a stalemate.
As Akira continued dodging and counterattacking Nakime, only one thought echoed in his mind.
"Seriously… where the hell are you, Yushiro? How much longer do I have to buy time for you?"
Yes, Akira was deliberately buying time.
To be honest, if he truly wanted to, he could kill Nakime right now. His Star Breathing First Form was far too fast; she would be dead before she even realized what had happened.
But he couldn't do that.
Nakime controlled the Infinity Castle itself. If she were killed outright, there was a high chance this entire dimension would collapse, along with every Demon Slayer trapped inside it.
That would be catastrophic.
So, Akira followed the same strategy used in the original timeline, Yushiro would hijack Nakime's brain and seize control of the Infinity Castle.
That was why Akira hadn't even drawn his cool new swords.
That's why he was holding back.
That's why he kept attacking passively, dodging, countering, stalling.
From the outside, it probably looked like a fierce battle between two evenly matched opponents.
In reality, it was a carefully controlled delay.
Akira waited for Yushiro to make his move, but for some reason, he was taking far too long.
Just then, Nakime hurled multiple buildings toward him at once.
Akira retaliated instantly, punching out shockwaves that shattered the incoming pillars, sending wooden rubble flying in every direction.
And then, out of the corner of his eye, he saw him.
Yushiro, sprinting toward Nakime.
He was invisible, but Akira's Mystic Eyes of Truth pierced straight through the concealment.
"Good. Finally."
Akira tightened his stance and decided to push harder.
If Yushiro was finally in position, then all Akira had to do now was distract her just a little longer.
Using his superior mobility, Akira weaved through the storm of incoming attacks and finally closed the distance.
Power gathered into his fist.
"Destructive Death—Eight-Layered Demon Core."
He charged the attack, muscles tightening as energy compressed to a terrifying density. He was just about to unleash it, but Nakime reacted instantly.
She plucked her biwa again and again, summoning more and more towering room-pillars, stacking them together to form a massive shield in front of her.
Just as Akira was about to release the attack.
The pillars stopped.
Mid-motion.
They froze in place as if time itself had stalled.
Akira's eyes widened slightly.
He turned his gaze and saw it.
Yushiro had finally crept up behind Nakime.
A blood talisman was pressed firmly against her body.
"…Finally," Akira muttered. "Where the hell were you?"
Yushiro snapped back immediately, irritation clear in his voice.
"The hell? Can't you distract her without destroying everything around you?! Do you have any idea how hard it was to dodge all those stupid attacks and random broken debris? Think about others when you fight!"
Akira coughed lightly, suddenly realizing just how much of a mess he'd made.
"Well… sorry about that," he said awkwardly. "What happened happened. Anyway, how's the control?"
"It's fine," Yushiro replied. "But cut off the connection before Muzan wakes up."
"Got it."
Akira reached into his inventory and pulled out an injection, then swiftly drove it into Nakime's neck.
It was something he had created with Tamayo, a compound designed to sever the connection between a demon and Muzan himself.
In the original timeline, Muzan had immediately killed Nakime the moment he realized she'd been compromised.
But now, that wouldn't happen.
Now, Akira could control Nakime.
And with her, control the battlefield itself, minimizing casualties across the Infinity Castle.
Akira exhaled softly.
"Where's Muzan? Is he awake?"
Yushiro shook his head. "No. I'm still searching. But it looks like Erika is fighting Upper Moon Rank One right now."
Akira froze.
"…What?"
He screamed, "WHAAAT?!"
"Why didn't she invite me? Did she forget to contact me again?!" Akira, though sadly.