Imperium of Man Terra Aeterna Season 01: Rise of Humanity's War Machin

Kanae remained silent the entire way back.

"....."

As she led Reuel and the others back to the Demon Slayer Corps headquarters, her mind was in chaos. She was still mourning her fallen comrades, and simultaneously overwhelmed by the sheer destructive force of Richelieu's naval salvo that had obliterated everything in its path.

She couldn't comprehend the kind of power that had just been unleashed. Reuel's explanation sounded more like a fairy tale to her—too foreign, too extraordinary.

"Sis!!"

A cheerful voice called from afar. A black-haired girl with purple-tinted ends and butterfly ornaments in her hair came running over.

Shinobu Kocho.

At this point in time, she was still a young girl—bright, honest, and a little competitive.

"What about the others?"

"We encountered Dōma," Kanae replied, her voice heavy. "Rank Two of the Twelve Kizuki. The others… didn't make it."

Her tone grew quieter as she spoke to her little sister. The sorrow she had been holding back finally started to leak into her words.

Shinobu simply lowered her head.

"I see…"

She understood. The mortality rate among Demon Slayers had always been high. Since the day they picked up the Nichirin Blade, they had all accepted this risk.

However, moments later, the silence was broken by a startled voice from one of the Corps members who spotted Reuel and his group.

"Wait… You met the second team but came back alive? You mean… who the hell are these people?"

All eyes turned toward the unfamiliar guests standing calmly behind Kanae.

Reuel stepped forward and greeted them with poise. "Hello. We come from another world. Our mission is to kill the Twelve Kizuki… and Kibutsuji Muzan."

---

About thirty minutes later, all senior members of the Demon Slayer Corps had gathered. They didn't greet Reuel and the shipgirls with suspicion, but rather… like emissaries from the imperial court or nobles from some celestial palace.

Not without reason.

In the eyes of the Demon Slayer Corps, killing fifty regular demons or defeating a single Kizuki member was already enough to be promoted to Hashira, the highest rank in the Corps' hierarchy.

And Reuel and his group had taken down Dōma in mere seconds.

To them, it was as if gods had descended from the heavens in human form.

Though there had initially been doubts from some of the more conservative members, those reservations vanished the moment they heard Kanae's full account—along with her personal guarantee.

They shared the same enemy.

Demons.

So technically… they were now allies.

Both parties sat cross-legged on tatami mats. Support staff from the Corps served warm tea, fruits, and some simple sweets. This rare moment became a historic meeting of two vastly different worlds.

Shinobu, still curious, leaned toward Richelieu.

"Sis… how did you beat Dōma?" she asked, wide-eyed. "What kind of weapon did you use? I didn't see a Nichirin sword on you."

Richelieu answered flatly, "Quadruple 380mm Mle 1935 artillery. Equipped with armor-piercing and high-explosive 16-inch shells."

"???"

Shinobu stared blankly at her sister.

Kanae shrugged. "Don't ask me. I don't get it either."

Not long after, another member spoke up—a young man with fiery blond hair and a burning aura: Rengoku Kyojuro.

"What breathing technique do you train under? Your power is astounding. Even I—who practice Flame Breathing—can't match your presence."

Belfast responded politely, "We're powered by mind cubes and reactors. Hydrogen fusion reactors, to be precise. Essentially, it's the fusion of hydrogen nuclei—similar to the core of a star—used to produce clean and limitless energy."

"???"

Rengoku looked at her like he had just heard a foreign incantation. The concept of a reactor was obviously far beyond the grasp of anyone living in the Taisho era.

Silence. Stillness.

Reuel finally spoke up, breaking the deadlock.

"All right. Let's discuss the main topic: the strategy for killing demons."

Seeing how the conversation between both sides had devolved into a classic case of chicken and duck, Reuel decided it was time to take over the discussion.

"As you've seen, one of our missions is also to kill Kibutsuji Muzan and the remaining Kizuki," he said calmly, but with unmistakable resolve. "I believe we share the same goal."

"That is correct."

A gentle yet commanding voice came from the back room. A young man with a pale face and a frail body stepped in slowly.

Ubuyashiki Kagaya—Leader of the Demon Slayer Corps.

"The Demon Slayer Corps was established from the very beginning to destroy Muzan," he continued. "My family has been hunting him for nearly a thousand years… but to this day, we've never succeeded."

His voice remained calm and composed, though the weakness in his body was obvious. Yet his presence as a leader never wavered.

"If there's anything we can do to help," Reuel asked, "do you know Muzan's current location, or that of the remaining Kizuki?"

Kawakaze, standing beside him, added, "We're ready to move right now if needed."

But Ubuyashiki Kagaya only shook his head gently.

"Their whereabouts are difficult to track. Upper-rank demons rarely show themselves. Even when they do, it's usually us being hunted—not the other way around."

He took a short breath, bowed his head for a moment, then continued.

"Often, when our members encounter powerful demons… they're killed before they can send a report. There's no time to call for help."

Exactly the kind of situation Kanae had experienced.

Sudden encounters with high-level demons typically ended in tragedy—no chance to retreat or request backup.

Reuel folded his arms, thinking for a moment.

"That means we need to draw the snake out of its hole…"

His eyes narrowed sharply, full of calculation.

"With so many demons scattered across different locations, hunting them one by one isn't practical. It'd be more efficient to lure them all to one place."

"Eh?"

Several Demon Slayers turned with startled expressions.

Reuel continued in a relaxed but confident tone, "Maybe we should create a situation… that forces Kibutsuji Muzan and the remaining Kizuki to confront us directly."

The room instantly fell silent. The Demon Slayers' expressions shifted dramatically.

Usually, facing even a single high-level demon was a nightmare for any team. And this man… wanted to gather all of them at once?

"Ahem…"

One of the Hashira finally spoke up. "Lord Reuel, Kibutsuji Muzan is no ordinary demon. Even legendary swordsmen like Tsugikuni Yoriichi couldn't kill him completely. Please do not underestimate his power."

Ubuyashiki added cautiously, "Perhaps… there's nothing in this world that can kill him, except the Sun Breathing technique… and sunlight itself."

Reuel was silent.

In his heart, he thought—perhaps that's true… from this world's perspective.

But he came from a very different universe. He had the Imperium of Man, the Imperial Navy, and elite troops who could fight literal gods of Chaos.

And now they were telling him he couldn't kill… just one Kibutsuji Muzan?

He suppressed a faint smirk and nodded, keeping his thoughts to himself.

"So you're saying only sunlight can kill demons?" he asked, still composed. "That theory makes sense… and as it happens, we might be able to work with that."

Everyone turned toward him.

Reuel gave a faint smile. "What is the sun, really? A giant ball of fire fueled by hydrogen fusion, constantly radiating thermal and ultraviolet energy. Light that can burn demons to ash."

He glanced at the ceiling, as if imagining something. "We don't need to create a new sun or build a death star like in fiction… We just need to utilize the technology we already have."

"Huh…?" One of the Corps members couldn't hide his astonishment.

"Even if Kibutsuji Muzan has absurd vitality and can only be killed by sunlight… we can, technically, create a 'miniature sun' strong enough to send him and his minions straight to hell."

Silence returned to the room.

They... didn't know whether to be terrified, awestruck, or just assume Reuel was insane.

Create a sun?!

"Is… is there such a weapon?" one Hashira asked, his voice hoarse.

"What's it called?"

Ubuyashiki's eyes narrowed sharply. For the first time, a glimmer of both intrigue—and caution—appeared in his soft gaze.

"Hydrogen bomb," Reuel replied calmly. "And that's just one example. But… honestly, if I explained everything, it would probably only confuse you further."

"Ah…"

The Hashira and the Demon Slayer Corps staff could only gape in stunned silence.

The Demon Slayer Corps were genuinely curious about how to create an "artificial sun" to destroy the Oni.

Unfortunately, given their cultural and scientific limitations, understanding the concept of nuclear fusion was no less difficult than humanity on Earth trying to comprehend a single drop of water from Trisolaran civilization.

Even though Reuel had tried to explain everything in the simplest terms possible, the expressions on the Demon Slayers' faces didn't change—like babies seeing the world for the first time.

Butterfly Kanae and Butterfly Shinobu couldn't help but scratch their heads in frustration.

"Ugh… why is my head so itchy?" Shinobu muttered quietly.

"I feel like my brain is literally trying to grow," Kanae mumbled beside her.

Fortunately, they all managed to distill one simple truth: even if the Demon Slayers couldn't defeat Muzan, as long as Reuel, the Imperium of Man, and the ship girls were on their side—victory was no longer a possibility, but an inevitability.

Their mission was now clear: find Muzan and the remaining Kizuki. The rest? Leave it to the Imperial Guard.

Seeing how easily Richelieu had obliterated Dōma, the Upper Rank Two Kizuki, it was obvious that no one among the Twelve Kizuki could match them.

"So, our question now," said Reuel, glancing around, "is how do we find Muzan and the remaining Kizuki?"

Everyone began to ponder.

As the mastermind behind the world of Kimetsu no Yaiba, Kibutsuji Muzan had survived for more than a thousand years. Not just because of his power, but due to one defining trait:

He was a coward.

And extremely cautious.

Usually, Muzan hid in the shadows, manipulating his subordinates from afar. The moment things turned unfavorable, he would vanish like smoke in the wind.

Even during the Sengoku Era, after getting utterly thrashed by Tsugikuni Yoriichi, he didn't dare to show himself until he was absolutely sure that swordsman was dead.

Reuel suspected that after hearing about Dōma's death, Muzan would resort to his old tricks—vanishing again into thin air. For all he knew, the bastard might be digging a hole deep in some remote mountain forest, and wouldn't surface again for years... maybe ten... maybe even eighteen.

The only extreme solution? Bombard the entire Japanese archipelago.

But unfortunately, that would likely wipe out the civilian population as well.

And they could eventually be recruited as citizens of the Imperium of Man.

"I can't waste my time in this world just to chase one cowardly creature," Reuel thought, sighing quietly.

"Maybe we can spread more Demon Slayers across the country?" Kanae suggested.

"If there's any sign of Muzan or the Kizuki, we'll immediately send a signal, and you, Lord Reuel, will come with your troops for support!"

"Too risky," Ubuyashiki shook his head slowly. "Even senior swordsmen can be killed before they have the chance to send for help. In most cases, Oni kill incredibly quickly."

"Then how about we use air support from the carriers?" Kawakaze chimed in enthusiastically. "Once the ground team spots an Oni, we attack from the sky! There's no way they can survive a bombing run, right?"

It was a reasonable plan. Especially considering they had three aircraft carrier ship girls with hundreds of recon planes and bombers. Their strike range could cover vast territories.

"You've been hanging around Essex, haven't you?" Reuel gave a faint smile but shook his head. "Still... there just aren't enough Demon Slayers. And Japan is far too vast. We're still basically looking for a needle in a haystack."

Silence. No one could argue with that.

Everyone went back to thinking hard, but no effective solution emerged.

Reuel held his chin, trying to recall the story arc details from the original Kimetsu no Yaiba.

The Swordsmith Village… The Infinity Fortress…

He tried to immerse himself in Kibutsuji Muzan's mind.

If only that coward would show himself to me, I'd destroy him instantly with the Emperor of Mankind's psionic might…

But alas, reality wasn't that convenient.

Kibutsuji Muzan was both cowardly and cunning. He wouldn't appear just because someone taunted him.

And then suddenly… an idea struck.

"If we can't find the Oni… why don't we make the Oni come to us?"

"Huh?"

The room was suddenly filled with confusion. Even Shinobu Kocho stepped forward, eyebrows furrowed.

"You mean… how can we possibly flip the situation that drastically?"

Reuel raised two fingers, signaling them to stay calm.

"Think about it. What are the two things Kibutsuji Muzan desires most?"

"First, to find the Blue Spider Lily and create a serum that allows Oni to withstand sunlight. With that, he'll achieve true immortality."

"Second, to annihilate the entire Demon Slayer Corps and anyone who could pose a threat to him. That way, he can live freely without fear."

"From those two goals, we can craft two bait scenarios."

Unlike humans, Oni possessed both biological and supernatural advantages: physical endurance, speed, reflexes, and magical abilities. But they also shared one absolute weakness:

The sun.

Even Muzan, the oldest of the Oni, could not escape that curse. For a thousand years, he had worked tirelessly to overcome it. And because his fear of death was so overwhelming, anyone who posed even a potential threat to him was swiftly exterminated.

That was why he had all users of Sun Breathing wiped out after Yoriichi's death. He wanted that legacy erased—permanently.

Cruel and cowardly. Cunning, yet impulsive.

Kibutsuji Muzan was a creature of contradictions.

"We've never really stopped to think about… what Muzan actually wants," Shinobu murmured quietly.

"What you're saying makes sense."

Ubuyashiki nodded slowly, followed by the Hashira and the other officers. They were starting to realize that Reuel seemed to possess an incredibly—almost suspiciously—deep understanding of this world and the Oni.

He knew details even the experts couldn't confirm.

Where exactly had he gotten all this information…?

"So," Ubuyashiki muttered, deep in thought, "based on the two points you mentioned… there are only two ways to lure Kibutsuji Muzan and the Twelve Kizuki out into the open."

He raised one finger after another.

"First, find the Blue Spider Lily."

"Second, use the Demon Slayers themselves as live bait, actively drawing them out."

"If both things are done at the same time… Muzan will likely come on his own, wouldn't he?"

"Brilliant!" Reuel immediately gave a thumbs-up, grinning with full approval.

Though Ubuyashiki's body seemed frail, his mind was razor-sharp.

"And the best course of action," Reuel continued calmly, "is to merge both strategies into one maneuver."

He waved his fingers in the air, as if sketching a grand plan. "Picture this—the legendary, incredibly rare Blue Spider Lily is placed at the Demon Slayer Corps' main headquarters. The very same place where the strongest swordsmen are gathered."

"To Muzan, it'll look like a gift from the heavens: a chance to massacre his enemies and claim the item that might finally free him from the curse of sunlight."

"How could he possibly resist such a sweet invitation?"

"And when the time comes," Reuel grinned, his tone now tinged with irony, "he'll make his grand appearance in true theatrical fashion. Bringing his entire 'family' and Oni offspring from across Japan, proclaiming the rise of the Oni, and launching a glorious assault—like a bloody traditional opera."

"....."

Everyone present fell silent.

Even the ship girls standing beside Reuel—usually composed even in chaos—now stared at him with puzzled, slightly worried expressions.

Commander… why do you know so much about Kibutsuji Muzan?!

And why does this plan sound like a death trap for everyone?

But Reuel merely offered a faint smile, choosing not to answer questions that were never asked aloud. How could he possibly explain that these girls came from a game, and the Demon Slayers were just comic book characters he'd read about in a previous life?

He could be honest with the women from the Resident Evil universe. They were his, now.

But with these ship girls—so kind, loyal, and full of spirit—he couldn't bring himself to shatter their world.

As for the people of Kimetsu no Yaiba… ah, forget it. They were simply potential citizens for the Imperium of Man. No matter how strong they were, they still couldn't compare to the unwavering might of the Imperial Guard.

And now? Reuel was no longer just an ordinary man.

He was the Emperor of Mankind himself.