Crossover Shipgirls: Building a Dimensional Empire from Scratch

Just outside a small town, in the desolate countryside—

A young girl in a Demon Slayer uniform with black hair and violet eyes, adorned with butterfly-shaped hairpins, was desperately dodging attacks.

Her body was riddled with wounds, and her uniform, along with the butterfly-patterned haori draped over her shoulders, was soaked with blood.

Nearby, several corpses clad in Demon Slayer uniforms lay scattered. Their deaths were horrifying, suggesting that they had suffered brutal attacks.

"Cough… cough…"

Kanae Kocho gripped her Nichirin blade tightly, forcing herself to stand.

Her gaze locked onto the man standing a short distance away—a young man with rainbow-colored eyes and white hair.

Upper Rank Two of the Twelve Kizuki, Doma.

Kanae could never have imagined that what was supposed to be a routine demon extermination mission would lead to an encounter with the second-highest-ranking demon among the Twelve Kizuki.

Her team had been utterly overwhelmed, slaughtered in the blink of an eye.

"Come now, find your release and ascend to paradise with me," Doma said, spreading his arms wide in a mock embrace.

Though his expression feigned pity, it carried an unsettling hint of malice.

"Like hell I'll go to your paradise!"

Kanae spat out a mouthful of blood and cast a glance toward the pitch-black night sky.

If only she could hold out until sunrise, there might be a slim chance of survival.

Demons feared sunlight and could only operate during the night.

But judging by her current state, she wouldn't last another moment.

"Is that so…?"

"How boring. If you die, you'll fade into nothingness, unable to feel anything at all."

"But if our flesh becomes one, you'll gain eternal life."

Doma stepped forward, his tone almost gentle.

By "becoming one," he meant devouring her. As a demon, his greatest pleasure lay in consuming humans.

"No…"

Kanae gritted her teeth, forcing herself to stand. She assumed a fighting stance, ready for a desperate last stand.

Suddenly—

Vroom.

A low droning hum echoed through the sky.

"What is that?"

Doma tilted his head, puzzled.

He had slaughtered or devoured everyone in this village. Where could any survivors have come from?

Both Kanae and Doma instinctively looked up.

Vroom. Vroom.

Three single-wing propeller planes circled overhead.

"???"

At this point in the Demon Slayer world, aviation technology was nonexistent.

Neither Doma nor Kanae could comprehend the sight of these metallic birds in the sky, leaving them utterly bewildered.

Rat-a-tat-tat!

The planes locked onto Doma and dove toward him, strafing the area with machine gun fire. The large-caliber rounds shredded the wooden buildings around him and kicked up a cloud of dust.

Splurt.

Doma had never imagined that after years of battling Demon Slayers on the ground, he would one day face an aerial assault.

"This… what is this?"

Kanae, sitting on the ground, stared at the sky in utter confusion.

"Experimental carrier-based aircraft, BF-109G," came a calm voice.

"!"

Kanae startled and turned her head, only to find herself surrounded by several strangers.

They were all clad in black-and-red uniforms. At the center of the group stood a young man, flanked by five strikingly beautiful women.

"They're gorgeous…"

For a moment, Kanae was entranced, but she quickly shook her head to regain her focus.

"No, no… excuse me, but who are you?"

"Demon Slayer Corps? No… the Shogunate?"

The uniformity of their attire led Kanae to assume they belonged to some organization.

"If not the Demon Slayer Corps, then they must be from the government."

"We're neither," Setsuna said, helping Kanae to her feet.

He glanced at her and the desolate surroundings.

Their arrival appeared to have been a few years before the main events of Demon Slayer, preceding Muzan's massacre of the Kamado family.

This earlier timeline offered opportunities to save more people, but it also presented a challenge—there was no telling where Muzan might currently be hiding.

As the dust settled—

Crack. Crack.

Doma slowly rose from the ground, adjusting his neck and moving his limbs with a mechanical stiffness.

He glared at Setsuna's group.

Despite the strafing run from the aircraft leaving him in disarray, his demonic regenerative abilities and immense physical resilience allowed him to recover quickly.

"Die," Doma said softly.

He didn't care where these people had come from.

As a demon, his sole joy was consuming humans—literally.

Kanae, with her gentle and delicate appearance, likely tasted delicious.

The other women? Even more beautiful. Surely devouring them would bring unparalleled satisfaction.

Click.

Doma clapped his hands together, activating his ultimate technique.

"Blood Demon Art: Rime - Water Lily Bodhisattva!"

Boom!

A towering, ten-meter-high figure of a Bodhisattva materialized behind him, crafted entirely from ice and clasping its hands in prayer.

The surrounding temperature plummeted by several degrees.

Whoosh!

The icy Bodhisattva exhaled a frigid mist, freezing everything within a ten-meter radius.

Any human exposed to this frost would be instantly frozen, their bodies invaded by ice crystals, leading to respiratory failure.

"Ah…!"

Kanae shivered uncontrollably. She had known of Doma's ice-based Blood Demon Arts but had never imagined he could unleash something this overwhelming.

Even standing at a distance, the cold emanating from the Water Lily Bodhisattva was unbearable. If she got any closer, her blood would freeze solid.

The terror of Upper Rank Two was far beyond anything she had imagined.

"Starting off with your ultimate move, huh? Bold of you."

Setsuna tilted his head, studying the Water Lily Bodhisattva.

Thanks to the Wisdom Cube's enhancements to his physique, he felt no discomfort—just a slight chill.

"Richelieu, handle this."

"Understood."

Clack.

Richelieu stepped forward and materialized her rigging.

The silver-white cannons adorned with golden filigree radiated an air of majesty and divinity.

The twin quad-barreled turrets aimed directly at Doma and his Water Lily Bodhisattva.

Though the icy construct towered over Richelieu, nearly ten times her size, she remained composed and unwavering.

"Careful! Guns won't work on him!"

"Only a Nichirin blade can decapitate a demon!"

Kanae called out urgently, based on her own experience. The mysterious woman's weapon resembled a firearm, and she feared it would prove useless.

"That's not a gun," Setsuna corrected.

"It's a naval cannon."

"W-what?" Kanae was dumbfounded.

Boom! Boom! Boom!

Richelieu's quad 380mm main guns roared to life.

The shells, initially no larger than fists, streaked through the air before detonating as high-explosive rounds against the Water Lily Bodhisattva.

Boom!

The explosion's shockwave leveled much of the village.

In naval combat, Richelieu-class battleships could pierce the armor of enemy ships from over 20 kilometers away.

Each high-explosive shell carried over 70 kilograms of payload, capable of obliterating fortified ground defenses.

Enhanced by the Wisdom Cube, the firepower reached even greater heights.

The Water Lily Bodhisattva's defenses were laughable compared to naval-grade armor.

In the first instant of impact, the icy construct shattered into countless fragments.

Doma himself had no time to react before being engulfed by the thousand-degree firestorm.

"Ahhhh!!!"

A bloodcurdling scream echoed in the distance.

Boom!

The fiery shockwave created a blazing whirlwind, illuminating the night sky for miles.

It took nearly fifteen minutes for the inferno to subside, leaving behind a massive crater over ten meters deep.

"…"

Kanae stared blankly at the scene, utterly stupefied.

Never in her life had she witnessed such destruction.

Was this magic? A weapon?

Could this even be considered human technology?

Upper Rank Two, who had summoned such a colossal Water Lily Bodhisattva, was annihilated in mere seconds.

"Uh… where's Doma?" she asked cautiously.

"Probably scattered across the sky and ground," Setsuna replied nonchalantly, glancing around.

...

As they returned to the Demon Slayer Corps' base, Kanae was still in a dazed and confused state.

Part of her was grieving the loss of her teammates, while another part remained awestruck by Richelieu's naval artillery barrage.

She couldn't comprehend such overwhelming power, and no matter how Setsuna tried to explain it, the concepts eluded her completely.

"Onee-chan!"

A young girl with dark purple hair and butterfly-shaped hairpins rushed over to Kanae.

Shinobu Kocho.

At this time, she was still an outspoken, competitive young girl.

"What about the others?"

"We encountered Upper Rank Two, Doma… They…"

Kanae's voice grew heavy, her tone filled with sorrow.

"I see…"

Shinobu understood.

The Demon Slayer Corps suffered heavy losses as a matter of course. Death was something they had long accepted from the moment they picked up their Nichirin blades.

"Wait, you encountered Upper Rank Two? But you came back alive? That means…"

Another Corps member's eyes widened as they glanced behind Kanae at Setsuna and his group.

"These people are…?"

"Greetings."

Setsuna nodded in greeting to the members of the Demon Slayer Corps.

"We come from another world, here to physically purge the Twelve Kizuki and Kibutsuji Muzan."

Roughly thirty minutes later.

The higher-ups of the Demon Slayer Corps had all gathered to receive Setsuna and the shipgirls with the utmost courtesy.

The reason was simple: by the Corps' standards, killing fifty regular demons or defeating a member of the Twelve Kizuki was enough to become one of the highest-ranking officers, the Hashira.

Setsuna's group had obliterated Upper Rank Two, Doma, as if it were child's play. To the Corps, it was as though gods had descended.

Initially, a few members remained wary of the newcomers. However, Kanae vouched for them, and her vivid account of the events quickly dispelled any doubts.

They had saved Kanae from Doma's clutches, and more importantly, they shared a common enemy: demons.

In this light, they were natural allies.

Everyone sat cross-legged on tatami mats as the Corps' support staff served tea, fruit, and snacks, facilitating an exchange between two worlds.

"Onee-san, how exactly did you destroy Doma?"

Shinobu Kocho, her curiosity piqued, sat beside Richelieu.

"What kind of weapon did you use? I didn't see a sword on you…"

"Quadruple 380mm naval guns, Model Mle 1935, equipped with 16-inch capped armor-piercing and high-explosive shells," Richelieu replied matter-of-factly.

"???"

Shinobu's expression was one of complete bewilderment.

She turned to Kanae for help, but Kanae simply shook her head, equally mystified.

"What kind of breathing technique do you use?"

A blonde Corps member couldn't help but ask.

From his instincts alone, he could tell that these people possessed extraordinary physical strength, likely far surpassing even his own Flame Breathing technique.

"We rely on the power of cubes and reactors. You know, reactors? nuclear fusion?"

Belfast, trying to explain, briefly touched on the concepts of fusion and fission.

"???"

Kyojuro Rengoku blinked, utterly lost.

The concept of a reactor was far too advanced for someone from the steam age; he couldn't even begin to grasp the principles involved.

"…Perhaps we should focus on discussing how to kill demons instead," Setsuna interjected, taking control of the conversation as it became increasingly convoluted.

"As you've seen, one of our objectives is to eliminate Kibutsuji Muzan and the Twelve Kizuki. I believe we share this goal."

"Indeed," came a soft yet resolute voice.

A young man with a disfigured face and frail build stepped out from an inner room.

Kagaya Ubuyashiki, the leader of the Demon Slayer Corps.

"Eliminating Muzan has been the purpose of the Demon Slayer Corps' existence for nearly a thousand years," he said politely. Despite his weak body, his demeanor was calm and composed.

"Is there anything we can do to assist you?"

"Do you know the current whereabouts of Muzan or the remaining Kizuki?"

Illustrious eagerly chimed in.

"We don't," Kagaya replied, shaking his head.

"Demons are inherently elusive, and the Upper Ranks and Muzan are even more so. They rarely show themselves."

"Even when they do, it often catches us off guard, resulting in severe casualties."

As Setsuna expected, the real challenge wasn't defeating the demons—it was finding Muzan and the other Kizuki.

Japan wasn't a particularly large landmass, but if Muzan actively chose to hide, tracking him down would be no easy task.

"In fact, we may have encountered Upper Ranks numerous times, but the teams involved rarely had the chance to report back."

"By the time reinforcements arrived, the demons had already slaughtered everyone," Kagaya lamented.

Much like Kanae's earlier encounter with Doma, many Corps members were silenced before they could send word for help.

"So… we need to draw them out," Setsuna mused aloud.

"Having demons scattered across the nation and hunting them down one by one would be inefficient. If only we could gather them all in one place…"

"Perhaps we could devise a plan to lure Muzan and the remaining Kizuki into a final confrontation?"

"Ah?!"

The Corps members were stunned.

They were used to struggling against even a single Kizuki. The thought of deliberately gathering all the demons together was almost unthinkable.

"Cough, cough."

"Mr. Setsuna, Muzan is extremely powerful. Even Yoriichi Tsugikuni couldn't completely destroy him. Please, don't underestimate him," Kagaya warned gently.

"Besides the Sun Breathing technique and sunlight itself, there might be no other way to kill him."

"…"

"Sunlight is the only thing that can kill Muzan? That's an interesting theory—but something we can handle," Setsuna replied with a faint smile.

"The essence of sunlight is simple: a massive ball of hydrogen and helium undergoing constant fusion. Sunlight is just ultraviolet light and heat radiation."

"If Muzan's resilience truly necessitates sunlight to kill him, then we can just create an artificial sun to send him—and the rest of the demons—straight to hell."

"!!!"

The room fell silent as everyone held their breath.

Demons feared the sun, and this man claimed he could create one.

What kind of power was this?

With such technology, Muzan and the Twelve Kizuki would be reduced to mere ants.

"Such a divine weapon exists?!"

"What do you call it?!" Kagaya's eyes widened in shock, his voice hurried.

"A hydrogen bomb."

"…Huh?"