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

After the meeting between the ship girls and all departments within the Imperium of Man - including Ursarkar E. Creed - it was decided that the universe of Kimetsu no Yaiba would be officially integrated into the territorial domain of the Imperium currently being built by Reuel. At the moment this decision was made, Reuel himself had already moved on to the Resident Evil universe to handle a separate matter.

Ursarkar E. Creed immediately deployed to the military zone to mobilize the Cadia Shock Troopers, carrying out a direct mandate from God Emperor Reuel.

Meanwhile, Reuel confirmed the personnel who would accompany him on the conquest expedition to the new universe.

"Richelieu, USS Phoenix, Belfast, Enterprise, Prinz Eugen-come with me," said Reuel firmly.

"The rest will remain stationed on Terra Aeterna. ROC Yat Sen, while I'm gone, you'll handle all affairs here in my name."

The Imperial Guard forces led directly by Creed were given the primary mission: to conquer the entire planet within the Kimetsu no Yaiba universe. Construction of the Imperial Palace and an underground city had already begun, and several ship girls were assigned to assist with the building process.

"Understood. May the Commander's expedition proceed smoothly," ROC Yat Sen replied in a calm tone, full of quiet confidence.

Yat Sen's composure-her long-established hallmark-made her the perfect figure to lead and oversee the construction efforts. She was also tasked with coordinating the Universal Bulin and Manjuu deployed as construction labor.

"Eh-why are only they chosen? Take me too, Commander!"

"I wanna see another world too, Commander-chan~!"

Some of the unselected ship girls looked visibly disappointed, their pleading expressions doing absolutely nothing to help make the atmosphere feel more serious.

"..."

The Vanguard fleet consisted of 50 members. Aside from Akashi-who was busy with the construction of a Gundam and the design of future space warships-over 20 ship girls would be stuck on Terra Aeterna without any significant missions in the near term.

"Why are you all so anxious?" Reuel asked with a smile. "After this mission is complete, I'll open a permanent space-time channel. We'll establish a long-term stable relationship with the Kimetsu no Yaiba universe. You'll even be able to take walks or go shopping later-assuming there are no missions, of course."

The ship girls instantly erupted in cheers.

"Put on our combat uniforms, raise the banner of the Imperium. We're heading out."

"Let's give them-the people of Kimetsu no Yaiba-a little taste of technology."

---

Two days later, on a remote planet where the dimensional gate had opened...

Reuel stood tall before the portal with five ship girls by his side, all clad in black military uniforms. Behind them stretched the full might of the Imperium: hundreds of thousands of Imperial Guard units, ranks of Leman Russ tanks, Chimeras, and millions of Astra Militarum soldiers led by Chris Redfield. The sky above was filled with majestic Imperial Navy warships, floating as if guarding the very edge of reality itself.

Once again, the ship girls felt the immense weight-and pride-of their responsibility.

They were now official citizens of the Imperium of Man, representing Minato Port from Azur Lane, and serving as instruments of the Commander's will in this multiversal conquest expedition.

"I will definitely offer this universe to you, Commander... with my own hands!" declared Da Feng, her body trembling with overflowing excitement and anticipation.

"No matter who stands before you-be it an Oni King or something else-I'll destroy them without hesitation!"

"In any world you find yourself in, I will always protect you," said Belfast in her usual calm, nearly expressionless tone-yet filled with absolute resolve.

"All units in position." Reuel gave the signal to prepare. He opened his star map and selected the coordinates of the target reality: Demon Slayer: Kimetsu no Yaiba (Steam Age).

In that universe, an island nation was flourishing during the Taisho era. Its level of technology was somewhere in the middle of the Steam Age-with steam engines and firearms just beginning to be used in limited fashion.

There existed beings of extraordinary power known as "Oni"-creatures with combat abilities far beyond ordinary humans. Yet their weaknesses were just as glaring: sunlight was their natural enemy.

Cross-Universe Power Comparison:

Technology Level: Primitive - Equivalent to early or feudal civilizations.

Military Strength: Regional - Only capable of operations within a single planet or confined region.

Economic Power: Closed Economy - Total dependence on local resources.

---

Diplomacy.

Time Travel.

Declaration of War.

From the moment these two worlds first made contact, the balance of power shifted drastically. The combined military and technological strength of Azur Lane, Warhammer, and StarCraft utterly shattered the established order in the Kimetsu no Yaiba universe.

There was no point in even discussing the economy-the comparison was irrelevant.

The tech tree developed by the Imperium focused purely on military power.

Agriculture and light industry were barely developed-not even comparable to the local steam-era production systems.

Truly ironic. The Imperium could build Gundams, starships, and weapons of mass destruction-yet its agriculture was still in its infancy.

"A neighbor like this will be easy to dominate among the stars..."

Reuel activated the time-travel function of his system and focused energy into his hand.

"Open space-time channel: Imperium of Man - Demon Slayer: Kimetsu no Yaiba World."

Swish.

Space and time before the dimensional portal-resembling a Webway-began to distort.

A colorful channel tore through the dimensions, ripping through reality until a stable gate slowly formed.

"Let's annex the Kimetsu no Yaiba universe."

With a single wave of his hand, Reuel stepped into the dimensional corridor, followed by the five selected ship girls. Behind them, the main force marched through.

"Commander, good luck."

The ship girls left behind on Terra Aeterna waved from the central plaza.

Bzzzzzt-

A sensation of lost gravity and dizziness lasted about ten minutes. Afterward, their vision slowly began to adjust.

A group of six now stood on alien soil.

Before them lay a small, gloomy, and dilapidated village.

With gabled rooftops and fragile wooden structures, its architecture clearly reflected a classic Japanese style-completely untouched by modernity.

Reuel immediately instructed Ursarkar E. Creed and the Imperial Guard to disperse across the world to carry out the first phase of operations.

Meanwhile, Reuel and the ship girls remained in Japan-carrying out a mission assigned directly by Reuel's system.

"So... this is the world where demons hunt demons, huh?"

"Feels... incredibly backward."

One of the ship girls rubbed her temple and looked around in disbelief.

Night had fallen.

A chilling silence cloaked the entire area.

The old buildings on either side of the street were completely dark, not a single light source in sight.

A thin mist hovered low, adding a thick horror atmosphere-like they had just stepped into a scene from a Japanese thriller film.

"Smells like... blood in the air."

Belfast sniffed quietly, her brows furrowing.

Ship girls possessed senses far keener than ordinary humans.

They could detect spiritual fluctuations, thermal signatures. The moment they set foot in this world, the cold and the scent of blood hit them like a wave.

"Da Feng, deploy recon planes. I want full visual and thermal reports within a two-kilometer radius," ordered Reuel in a flat yet firm tone.

As the leader of the expedition into the Demon Slayer World, the first priorities were determining geographic location and timeline-two vital factors before any military strategy could be formulated.

With the military force they had brought, killing the Twelve Kizuki-or even Kibutsuji Muzan himself-would pose no real challenge.

But that wasn't the point. What mattered more was understanding the influence system that allowed beings like Oni to hide in the shadows-even in this low-tech era.

"Oni target detected. Data incoming-clear."

Two miniature aircraft carriers deployed from Da Feng's rear deck. They hovered autonomously and projected launch vectors.

A group of toy-sized recon planes emerged from internal compartments.

Once airborne and free from local gravity, the aircraft experienced micro-dimensional resonance-expanding back to full combat size.

A sharp drone filled the air.

The metallic birds shot off in all directions, their AI systems already synced with Reuel's tactical network.

It didn't take long.

Da Feng received the incoming transmission and raised her hand to her communication visor.

"Visual contact. Conflict point detected-320 meters northwest."

"One side appears to be a human team armed with katanas-likely demon slayers."

"And... the other side... uh..."

She hesitated, staring at the holographic tactical screen in her hand.

"Someone... a young man. Around twenty. Holding... a fan?"

Reuel frowned.

"A fan?"

"Yes, Commander. A large fan. But-his energy doesn't read as human. Could be an Oni or... something else."

Reuel looked up at the sky, now thickening with spiritual fog.

"Send a light recon team to the location. No contact. I want full footage before sunrise."

"Da Feng, you and Phoenix remain airborne on standby."

"The rest of you-stay ready for immediate intervention."

The ship girls nodded silently, activating their weapons without a word.

The first battle in this universe had just begun.

---

A young girl in a Demon Slayer uniform was fighting for her life. Her black hair was neatly tied back with a butterfly-shaped clip, while her violet eyes radiated determination despite her bloodied, battered body. Her butterfly-patterned uniform and haori were torn, soaked in blood.

All around her lay several corpses-fellow Demon Slayers who had met gruesome ends. Their wounds said everything about the brutality of the attack they had faced.

"Cough... Cough..."

Kocho Kanae gripped her Nichirin blade tightly, struggling to rise. Her body trembled, but her sharp gaze was fixed on the young man just ahead-a man with pale white hair and iridescent eyes, dressed in a lavish kimono with a fan in his hand.

Douma. Upper Rank Two of the Twelve Kizuki.

What was supposed to be a mission to exterminate a low-class Oni had turned into a trap laid by a high-ranking demon. Her comrades had been slaughtered almost effortlessly.

"Come now... Join me in eternal bliss."

Douma opened his arms, smiling wide, though his eyes gleamed with madness.

"Like hell I'd go to your heaven."

Kanae spat blood and glanced up at the dark sky.

If she could hold out until dawn, maybe... there was still hope.

But reality said otherwise. She knew she wouldn't last much longer.

"What a shame... Death is nothing but emptiness-no feeling, no meaning," Douma said, stepping forward slowly. "But if you merge with me, your body and soul will live forever."

The word "merge" in Douma's mouth was, of course, not metaphorical. It meant being devoured alive.

"No...!"

Kanae clenched her teeth and readied her stance.

If she was going to die, then she would die with her sword in hand.

And then suddenly-

Bzzzzzt-

A loud buzzing sound echoed from the sky. Douma looked up, brows furrowing.

"What... is that?"

All the villagers were dead. There shouldn't be a single living soul around. But that sound... it was unlike anything he had ever heard.

Alongside Kanae, he looked toward the sky.

Three metallic aircraft hovered above them-shaped like birds, with stiff wings, rotating propellers, and a deafening mechanical roar like some kind of flying monster.

"...Iron birds?" Kanae muttered, confused.

Neither humans nor demons in this world knew anything of aviation technology. The sight was as surreal as watching a mythical creature descend from the heavens.

Click. Click. Click.

The three aircraft locked on target, then dove sharply toward Douma.

Taka-taka-taka-taka!!

The deafening sound of machine guns rang out. Large-caliber bullets tore into the earth, obliterating the wooden houses around Douma and kicking up a storm of dust and debris.

Poof! Poof! Poof!

Douma leapt back at supernatural speed, stunned. After centuries of fighting humans from the ground, this was the first time he'd ever been attacked from the sky.

Shit...!

"What the fuck are these things...?"

Meanwhile, Kanae sat slumped on the ground, staring blankly at the sky.

"...What the hell was that...?"

Footsteps echoed from the edge of the forest.

"Carrier-based prototype aircraft, BF-109G."

Someone answered calmly, their voice steady and authoritative.

Kanae flinched. She quickly turned her head.

A young man emerged from the trees, surrounded by five young women with striking appearances and unfamiliar uniforms-neither Demon Slayer Corps nor Shogunate troops.

A double-headed eagle insignia was emblazoned clearly on their chests-a symbol Kanae had never seen before.

"...They're so beautiful..."

Kanae thought for a fleeting moment before shaking off her admiration.

"Excuse me... Who are you exactly?" she asked, still seated and gasping for breath.

"Demon Slayer unit...? No... Are you part of the Shogunate...?"

Her logic tried to tie their appearance to any military force she knew. But none of it fit.

"Neither," the young man replied.

He extended a hand and helped Kanae to her feet, then glanced around with a calculating look in his eyes.

This time travel felt strange.

It wasn't just a temporal anomaly-it was an intervention into the unwritten current of history.

In the timeline of Kimetsu no Yaiba, about two or three years before the story begins, Muzan Kibutsuji slaughtered Kamado Tanjiro's family.

The upside?

Those who had traveled through time now had the chance to save far more lives from the demons.

The problem:

Only God knew which dark corner Muzan was hiding in.

---

On the other side...

As the dust and smoke began to clear, a mechanical sound echoed.

Click... click...

Douma slowly rose from the ground. His body was still regenerating-his torn-apart hands beginning to fuse back together.

With a furious expression, he lifted his head and glared at Reuel and the mysterious group before him.

Even after being gunned down from aircraft and utterly devastated, a demon's body possessed resilience and physical power far beyond that of any human.

"Go to hell," Douma muttered, his voice cold and razor-sharp.

He didn't care who these people were or where they had come from. All he knew was-they were human.

And as a demon, his most primal desire was to devour humans.

Devour them literally.

Their flesh and blood were the peak of indulgence.

Kocho Kanae, with her gentle and warm appearance, looked like a sweet delicacy.

But the girls around Reuel... were far more beautiful, more alluring... and likely tasted far more exquisite on the tongue.

Click.

Douma clasped his hands together and activated his ultimate technique:

"Blood Demon Art: Frozen Sanctuary - Water Lotus Bodhisattva, Radiant Cold Stream!"

BOOM!

From behind his back, a colossal Ice Bodhisattva erupted, standing over ten meters tall, forming a divine silhouette with hands pressed together in prayer.

The entire statue was made of pure ice, and the air around it plummeted in temperature.

Fwoooooo-

The Ice Lily Bodhisattva unleashed a freezing mist, chilling everything within a radius of ten meters.

If that mist touched an ordinary human, they would freeze instantly. Ice crystals would pierce their respiratory tracts, causing acute internal necrosis.

"Ssssss..."

Kanae trembled violently. She knew Douma wielded ice as his Blood Demon element, but she had never imagined the demon possessed a technique this powerful.

The frigid air alone from the Bodhisattva stabbed into her bones. She knew-if she got even a little closer, her blood would freeze solid.

This was the terrifying might of the Upper Rank Two of the Twelve Kizuki.

"Attacking without a word... Interesting."

Reuel stared down the Ice Bodhisattva without the slightest fear. The extreme cold had no effect on his body-he was no longer made of mortal flesh. He was the Emperor of Mankind.

"Richelieu, handle him."

"Understood."

Ka-ka-ka-ka-ka-

Richelieu stepped forward, her form elegant and imposing in silhouette.

Her uniform resembled that of a high-ranking naval officer-shimmering white-silver with golden accents-a symbol of power and majesty.

Two quadruple main guns rotated into position and locked directly onto the Ice Bodhisattva.

"Careful!!" Kanae shouted.

"Weapons don't work on demons! The only way to kill them is to decapitate them with a Nichirin blade!"

She had no idea what kind of technology that stunning woman was using. But judging by the towers and elaborate structure, she guessed it was some kind of firearm.

"That's not a firearm. That's naval artillery," Reuel corrected calmly.

"Ha...?" Kanae blinked in confusion.

BOOM-BOOM-BOOM-BOOM!

All four 380mm main guns fired simultaneously.

In an instant, human-head-sized projectiles tore through the air.

Upon impact with the Ice Bodhisattva, the shells transformed into high-explosive bombs.

BOOOOOOMMMM!!!

The resulting blast carved out a massive crater and shook the entire area.

The shockwave leveled what was left of the village.

On the battlefield of the seas, Richelieu's guns could penetrate heavy-class battleships from over 20 kilometers away.

With the added power of Mind Cube technology, their destructive capacity was multiplied several times over.

Douma didn't have time to react.

In a single attack, his Ice Bodhisattva was utterly annihilated-shattered into fragments, melted, then vaporized.

The explosion unleashed temperatures exceeding a thousand degrees.

A surge of scorching wind formed a vortex of fire-a hellish tornado that lit up the night sky.

"AaaaaAAAARGGHH!!"

Douma's final scream rang out just before his body vanished into the cataclysmic blast.

Ten minutes later, the temperature began to drop, the smoke thinned, and at the heart of the battlefield...

...all that remained was a massive crater over ten meters deep.

Kanae stood frozen.

Her tongue was numb. Her legs trembled.

"Am I... dreaming?" she whispered.

"Douma... is dead...? Just like that...?"

"His body should now be scattered everywhere-in the sky, on the ground, and among the rubble," Reuel answered matter-of-factly.

---

Wattpad picture Depiction of the Imperial Palace being built within the Resident Evil world.