"Did you meet someone important?"
Akaza turned and looked at Tanjiro, who stood opposite him. There was still no shadow in the boy's crimson eyes.
"…Probably."
"Hiru once told me that when some people die, a powerful attachment can keep them lingering between life and death. They remain there, watching over the people they can't let go of. And when someone is caught between life and death themselves, they can see those souls watching over them."
Tanjiro raised his blade and pointed it at Akaza.
"To be honest, I've seen my father more than once. You could say he worries about me a lot. So there's no need to doubt what you saw. It was real, without question. Actually, it's because I've seen it myself and received help from it that I know it was real."
Akaza lowered his head and looked at his hands. They still seemed to carry the sensation of someone pulling on them.
"…Is that so?"
"That's right! But enough talking! I'm about to atta—"
"No need."
Akaza looked at the abruptly stumbling Tanjiro and gave a bitter smile.
"I've already lost. And… I no longer have any reason to keep fighting."
Tanjiro looked at Akaza's arm as it began crumbling into ash. After a brief pause, he smiled.
"I see. Then it's for the best if you've untied the knot in your heart. I'm sure they loved you. If you talk things through properly, then even if you can't go to the same place in the end, you'll still find peace."
"…I really do hate you."
"I don't like you either. And since we're enemies, that's fine!"
Akaza laughed out loud, ignoring Muzan's frenzied voice raging inside his mind. His golden eyes swept over Kyojuro and the other two, who still stood on guard, before settling once more on Tanjiro.
"You'd better not expect that guy to defeat Muzan. Compared to Muzan, he's far too weak... And like I said, demons are demons. They can never be the same as humans. In the end, you'll only become enemies."
"You're wrong. Hiru is extremely dependable. There's no way anything will happen to him!"
"No, that guy...!"
Thump.
Tanjiro instinctively turned and searched for the source of the sound.
It was unmistakably a heartbeat.
Such a powerful heartbeat...
Could it be Muzan?
Had Sensei still not found Muzan, while Muzan had already recovered from the damage he suffered?
"I take back what I said."
Akaza withdrew his gaze as well.
"That guy might actually be able to fight Muzan. But your Demon Slayer Corps' situation hasn't changed at all... Our plan may really have awakened a monster. If that guy is your greatest hope, then I suggest writing your wills now."
As Akaza's body completely disintegrated, Tanjiro frowned.
"So that was Hiru's heartbeat... I need to go check."
"Wait, Kamado boy!"
Kyojuro pressed a hand onto Tanjiro's shoulder.
"Explain things to us first! Who exactly is this Hiru, and why were our memories erased?"
"Hiru is Hiru. As for why your memories were erased..."
Tanjiro wore a troubled expression.
"Hiru really told me not to say anything, so please don't make this hard for me, Rengoku-san..."
Thump.
Sabito frowned.
"If you're not allowed to say it, then we'll go see for ourselves... Just what level of demon gives off such crushing pressure from nothing more than a heartbeat?"
"Hiru is a Primordial Demon, just like Muzan. I guess he released the suppression he'd been holding back all this time during the fight?"
"...Wait. Hold on."
Sabito stopped walking and pinched the corner of his eye.
"Didn't you just say you weren't allowed to tell us?"
"Hiru said I could tell you if you asked about his information."
Tanjiro tilted his head.
"That way, if something unexpected happens and Sensei isn't there, you'd at least be able to hold him back for a moment. But I'm not allowed to tell you anything about the missing memories."
"...Was he a Hashira?"
"Huh?! Giyu-san, did you remember something?"
Giyu sheathed his sword and sighed.
"…I don't understand."
"Hmm... That makes sense."
Sabito stretched his legs, now aching after relaxing.
"If he was a Hashira, then he should've been acknowledged. It really is impossible to understand what goes on inside a demon's head... Anyway, let's go take a look."
It wasn't only Kyojuro and the others. The other Hashira fighting throughout the Infinity Castle had also heard that heartbeat.
Obanai, who had just entered a focused state and was trying to use Aura to escape his predicament, felt every hair on his body stand on end.
"What is this... This disgusting feeling..."
"Iguro-san, could it be Muzan?"
Mitsuri smashed away a demon rushing toward them, worry written across her face.
"While you were concentrating, a crow came by and told us to break this Infinity Castle Blood Demon Art as quickly as possible. It said that if we don't hurry, everyone could be in danger."
"Hah... If we don't hurry, everyone could be in danger..."
Obanai turned his head, accurately locating Nakime through layer after layer of walls.
"I understand. I'll use everything I have."
"Yes! I'll do everything I can to support you, Iguro-san!"
...
"What the hell was that sound? A heartbeat?"
Uzui hefted his twin blades onto his shoulder, his previously carefree expression turning grim.
"Hey, hey... don't tell me that was Muzan's heartbeat. If it was, then I don't even want to imagine what kind of monster he really is..."
"It feels wrong..."
Yuichiro looked to the side with a tense expression.
"Has someone already started fighting Muzan?"
"Caw! The one fighting is not Muzan!"
"Could there be another Demon King?"
Muichiro lifted his gaze.
"Do we need to head there and provide support right now?"
"Caw! The highest priority is killing the demon controlling the Infinity Castle and moving the battlefield back to the surface!"
The Kasugai Crow flapped its wings urgently.
"Someone is already going to deal with the two Demon Kings! Please follow me at once! Caw!"
"Hey, Himejima, isn't this the backup plan Oyakata-sama mentioned before?"
Uzui followed after the crow.
"But using another Demon King as a backup plan is going a bit too far, isn't it?"
"Amita... Before Oyakata-sama departed, he only instructed this monk to make sure Tamayo was saved. Someone else would deal with Muzan..."
"Hey, hey... seriously?"
Cold sweat slid down Uzui's temple, though he still wore a smile.
"Creating one Demon King to deal with another. I've never heard of anything like that."
"Oyakata-sama must have had his reasons..."
Yuichiro's expression darkened as he looked at the crow leading the way ahead.
"And I don't know how to explain it. Even though my whole body feels uncomfortable after hearing that heartbeat, strangely enough, I don't feel any danger."
"Huh? Aniki, your instincts must be off. I'm completely creeped out."
"Mm... I don't understand it either. My body and my mind are giving me two completely different answers..."
"No matter what, let's do what the crow said first and kill the demon running the Infinity Castle. We can think about everything else afterward."
Uzui carried his blades in one hand while irritably raking the other through his hair.
"Having to watch out for rooms changing in the middle of a fight is beyond annoying."
...
"That sound... Is it Hiru?"
Yoriichi stood beside a well formed from overlapping houses. He looked back in the direction he had come from, then turned back and lowered his gaze to the massive lump of flesh crouched inside the well. Slowly, he drew his Nichirin Blade.
"Looks like I'll have to be faster."
The flesh mass seemed to sense Yoriichi's killing intent and immediately began pulsing like a heart.
Yoriichi did not hesitate. He leaped straight down from above, and with a turn of his wrist, the dazzling crimson Nichirin Blade cleaved through the flesh mass from top to bottom.
A sharp burnt stench filled the air, followed by Muzan's furious roar.
"Who?! Who is it?!"
Countless bone whips shot out from the flesh mass and lashed toward Yoriichi, only to be blocked in an instant.
Yoriichi looked at Muzan, whose chest had been torn open with a massive wound, and spoke in a low voice.
"The one who will kill you."
"Kill me? You think you are—!"
Muzan's voice cut off the moment he saw Yoriichi's face. More than fear, what filled him was shock.
"You're still alive?!"
Yoriichi had no intention of reminiscing with him. Crimson flames wrapped around the blade as he attacked again.
"Tsugikuni Yoriichi! If you kill me, that puppet will lose control immediately!"
Even so, the crimson blade still passed through his body.
In a single instant, the scene from years ago was recreated once more inside the Infinity Castle.
Yoriichi looked down at Muzan, who was barely keeping his severed head from falling.
The blade in his hand glowed an even deeper red.
"I will stop Hiru myself. But before that, I must first kill you completely."
His sword danced.
The surrounding rooms, which had been about to shift, were all cut apart in that moment. Muzan's Blood Demon Art, which was about to activate, was severed as well.
"Do you really not care about that puppet brother of yours?!"
Muzan had lost every trace of his usual elegance and shouted in panic.
"There are three people with him right now! The moment I die, Doma will destroy every remaining painting!
Do you think that man can suppress the urge to eat people?!
Maybe he's already eaten plenty behind your back!"
"...Hiru would never do that, even though he has had countless chances over these hundreds of years."
Yoriichi raised his Nichirin Blade.
"Hiru has lectured me countless times not to care too much for others. Yet he himself is the kind of person who would easily sacrifice himself for someone else... Hiru would never do such a thing."
"You think—!"
The crimson blade swept through Muzan's head and shattered it to pieces.
Only then did Yoriichi's cold voice sound.
"We were never greedy for lifespan as you are...
No, perhaps I am greedier than most. But all I desire is for this peaceful life to continue. I have not fallen so low that I would ignore the suffering of others and live by stealing from them."
Thump.
Yoriichi no longer looked at the flesh turning to ash. He sheathed his sword and rushed toward the source of the heartbeat.
"The others should be able to handle the remaining demons... Forgive me. Let me be selfish one more time."
...
Doma looked at Hiru before him, gently waving his folding fan. But the easy smile he had worn earlier was completely gone.
"Mm, mm... So this is Akiwa's true face? How frightening~
Now then, you three can relax a little~ I won't touch you anymore~
After all, look. Akiwa seems very hungry~
I wouldn't want to compete with Akiwa for food~"
Kanae did not dare relax, but her gaze still drifted toward Hiru.
Only the paintings on the last two walls remained. The murals on the other two walls and the ceiling had already been completely destroyed by Doma.
As the paintings were destroyed, even Kanae was shocked by Hiru's restraint.
More than once, she had felt killing intent fall upon her.
Yet Hiru had never attacked them.
But that restraint seemed to have reached its limit.
As the terrifying heartbeat rang out, that killing intent covered them once again, and for the first time since the battle began, Hiru turned to look at them.
After only a brief glance, however, he looked away again.
Those gray eyes settled back onto Doma.
"Thanks to all of you, I nearly forgot that I'm a Demon King."
"Mmmm~ You're too kind! I'm very happy to see Akiwa as well~"
Doma waved his fan.
"Akiwa must be starving, right? Look, there are three wonderfully nutritious girls right here~
Akiwa can enjoy them properly. Oh?
Akaza-dono seems to have failed~
How tragic~ He was my best friend besides Akiwa~"
Hiru raised a hand toward the remaining paintings and destroyed them all.
The aura around him grew even more chaotic, yet the expression that had seemed close to losing control instead became calm.
"Is that so? Which Upper Moons are still alive?"
"Mmm~ Looks like only Nakime and I are left."
Doma did not care at all that Hiru had destroyed the remaining paintings. His smile only widened.
"Say, Akiwa, won't you really consider being with me?
If Akiwa doesn't want to eat people, then I can eat them first, and Akiwa can eat me afterward~"
Hiru frowned slightly, disgust appearing on his face.
Just as he was about to speak, a loud crash suddenly came from behind him.
The solid ice sealing the room was shattered from the outside, and along with the fresh air came an irresistibly sweet scent.
The moment he smelled that fragrance, Hiru's hunger surged several times over.
He unconsciously looked toward the dust-covered opening and fixed his gaze on the scar-covered white-haired swordsman standing there.
"...Rare Blood?"
"Yeah, that's right! I'm Rare Blood!"
Sanemi's blade gleamed with a cold light, his expression savage.
"So you're the evil demon the crow mentioned? You don't look like much!"
Seeing Hiru raise his hand toward Sanemi, Kanae's sense of foreboding intensified.
But before she could speak, the crow perched on Sanemi's shoulder shouted loudly.
"You idiot! Jump now! Caw!"
Without a moment of hesitation, Sanemi immediately leaped high into the air the instant Kitaro ordered it.
The moment he moved, long gray crystal spikes erupted from the spot where he had been standing.
A moment later, they would have pierced him straight through.