Crossover Shipgirls: Building a Dimensional Empire from Scratch

”Hmph, bluffing. They gave me quite a scare.”

”Next time, I swear I’ll catch one of you, make her recite the Doctrine of Behavior eight hundred times—no, three hundred will do!”

After the shipgirls retreated, the Purifier remained stunned on the ocean for a long time before snapping back to reality.

In truth, the damage they caused wasn’t significant. Her main forces—battleships and aircraft carriers—were barely scratched.

As for the destroyed destroyers and frigates?

The Sirens had an unlimited supply. If she wanted, she could conjure a whole fleet with a snap of her fingers.

But the insult stung.

A few destroyers swinging glowing swords at her hull might not have left a mark, but the sheer absurdity of the scene left her fuming.

”Whatever, maybe they’ve been cooped up in the port too long and wanted to stretch their legs,” the Purifier muttered, soothing herself.

With no significant losses, she decided it wasn’t worth pursuing them.

The Next Day.

”Alert! Alert!”

The Purifier, basking in the sun, was startled awake by the blaring alarms.

”Enemy fleet detected 162 nautical miles southwest! Estimated force: 22 shipgirls, advancing at 36 knots!”

”?”

”Again?!”

She sprang to her feet, mobilizing her fleet to intercept.

This time, however, she noticed something odd—these shipgirls weren’t carrying shields or beam sabers.

They looked just like their usual selves, except… the bottoms of their rigs had a peculiar jet-like apparatus.

”Activate thrusters!”

Enterprise issued the command.

Whoosh!

The shipgirls, as if wearing rocket-powered backpacks, lifted off the water and ascended into the sky.

Hovering dozens of meters above the ocean, they deployed their rigs and began raining firepower down on the Sirens below.

Some of the larger aircraft carriers and battleships struggled with their massive rigs—causing their thrusters to falter. With a loud splash, they tumbled back into the sea, requiring rescue from their comrades.

”Ugh, I knew I shouldn’t have equipped the 460mm cannons… they’re way too heavy,” grumbled a certain vulpine shipgirl while wringing water out of her tail.

”…”

”Performance art?”

The Purifier was dumbfounded.

She’d seen planes fly but had never seen shipgirls soar through the air.

Before the Sirens could organize a counterattack, the shipgirls retreated once more, vanishing over the horizon.

”Second test: Light Pulse Propulsion System. Capable of short-term aerial maneuvering. Cannot sustain heavier rigs—excessive weight leads to failure.”

”Best suited for destroyers. Resource-intensive and energy-hungry.”

”Recommendation: Increase power output…”

As they retreated, the shipgirls jotted down notes on their findings.

”…”

”Did they drink too much coolant?”

The Purifier shook her head, bewildered.

Day Five.

”Charge!!! Capture the Big-Eyed Dumbass!!!”

A group of shipgirls charged forward, brandishing thermal axes for close combat.

Day Seven.

”Sniper positions! Pin her down!”

A squad of destroyers wielding oversized beam rifles peppered the Purifier with colorful laser shots from kilometers away.

The lasers couldn’t penetrate her armor but were blindingly annoying—like a disco ball spinning right in her face.

While they attacked, the shipgirls recorded more data.

”Fourth test: Beam Rifle (Type Maelstrom). Less effective than naval guns. Ineffective against Siren armor.”

”Recommendation: Develop higher-caliber versions…”

One week passed. Then ten days. Then half a month.

This strange cycle repeated itself.

The Purifier eventually grew accustomed to the shipgirls periodically showing up to harass her with their bizarre weapons.

Sometimes they managed to sink a few minor ships; other times, their weapons didn’t even scratch a frigate.

Resigned to the antics, she decided to let it be.

”Fine. Go ahead. Play around. It’s not like you can actually hurt me. Besides, we’ve got plenty of destroyers and frigates.”

Unable to catch them, the Purifier began treating the shipgirls’ antics as a form of entertainment.

Whenever she spotted them on the horizon, she eagerly wondered what quirky contraption they’d test next.

Gradually, an odd camaraderie developed between them.

The shipgirls refrained from excessive destruction, and the Purifier refrained from seeking revenge.

A Few Days Later.

”Shouldn’t we zap them with an EMP or something?”

A humanoid Siren floating nearby inquired hesitantly.

”What’s the point? We can’t breach the port anyway. Let them have their fun.”

The Purifier continued lounging on her rig, lazily splashing water with her hand.

”Besides, their new gadgets are pretty amusing. Weak, sure, but entertaining.”

”Look, they’re here again.”

She pointed toward the horizon, where another squad of shipgirls was approaching her domain.

”Let me see what new tricks they’ve cooked up this time.”

Placing her hands on her hips, the Purifier swam toward the incoming fleet.

”…”

The shipgirls exchanged glances, puzzled.

This Siren didn’t seem as hostile as the others. In fact, she could even speak coherently.

”Do whatever you want. None of your little toys can hurt me anyway.”

”If I’m in a good mood, maybe I’ll let you off the hook,” the Purifier taunted, smirking at Enterprise.

After weeks of encounters, she had a solid grasp of the shipgirls’ experimental weaponry.

The weapons were novel but lacked the firepower to pose a real threat. None of them could penetrate the armor of high-ranking Sirens like herself.

”Ready!”

Behind Enterprise, a group of shipgirls lugged out a massive cannon-like contraption.

The device was about five meters long, with a bore diameter around 300mm. It was bulkier than most battleship cannons and connected to a power supply unit.

”What, no rigs today? Just hauling a cannon?”

The Purifier raised an eyebrow.

”It’s a prototype. We don’t know if it works, so we didn’t integrate it into our rigs yet,” one shipgirl explained honestly.

”Oh. Go ahead, then.”

The Purifier shrugged, confident in her armor.

”She’s pretty chill. Are we sure it’s okay to test this on her?”

A few destroyer-class shipgirls whispered among themselves.

”High-ranking Sirens have incredible vitality. She’ll be fine,” retorted Prince of Wales dismissively.

”Apologies in advance.”

”Fire!”

Zzzzzzz!

The cannon hummed as it charged, its barrel glowing with a golden light.

”Energy weapon? You’ve outdone yourselves this time!”

The Purifier watched with curiosity, unfazed.

BOOM!

The massive recoil sent the cannon operators sprawling, nearly plunging them into the sea.

A torrent of red-gold energy erupted from the barrel, instantly vaporizing two Siren battleships in its path.

Their thick armor crumbled like paper before the high-energy beam.

Then, the beam struck the unsuspecting Purifier.

BOOM!!!

The resulting explosion launched her and her rig skyward, like a blazing meteor disappearing over the horizon.

”…”

The shipgirls squinted at the fading streak of light, saluting silently.

Then, they flipped open their notebooks.

”Test #16.”

”Model MGX-2235 Hellfire Beam Cannon. Effective against Siren battleships and high-ranking Sirens. Excellent firepower.”

”Drawbacks: Extremely high energy consumption and recoil. Best suited as a battleship main cannon.”

”Note: The high-ranking Siren in this region doesn’t seem very smart. Perhaps we could trick her into visiting the harbor someday.”

Earth.

Construction on the settlement was progressing steadily.

The production of Gundams was entirely under Akashi’s charge.

As for what weapons should be installed on the Gundams, there was a simple evaluation standard: any weapon that can damage Sirens is a good weapon.

If it could knock a Siren into the stratosphere, it was a great weapon.

Weapons that couldn’t even scratch a cruiser? They were simply useless.

The shipgirls from the harbor occasionally ventured out to hassle the Sirens, testing the combat effectiveness of these weapons in real scenarios.

They sent back the weapon data and experimental results, which were useful in two ways:

1. Helping the harbor upgrade its future weaponry.

2. Providing Akashi with references for deciding which components to install on the Gundams.

When Setsuna occasionally visited Akashi’s workshop, he found a variety of bizarre items on the design blueprints.

Things like particle cannons the size of battleship guns, or beam sabers over 40 meters long.

He couldn’t help but wonder what kind of monstrosity this repair ship was trying to build.

On another front, construction of the capital city had officially begun.

The ground was marked with white and yellow paint, dividing industrial, agricultural, and residential zones neatly.

The Bulins and Manjuus were hard at work building the city, starting from the industrial zone and working outward.

Above, reconnaissance planes buzzed through the air, assisting in construction by helping to map out exact locations. These planes were deployed by the aircraft carrier shipgirls, using their carrier-based aircraft.

”Bulin #0326! Your line is crooked!”

”That’s the main thoroughfare of the city! If you mess it up, it’ll drive perfectionists insane!”

Illustrious yelled through a megaphone, her tone as authoritative as a construction foreman’s.

”Burin?”

The startled Bulin immediately began correcting the line.

”Starting a city from scratch is such a hassle… And why am I stuck doing foreman duties?!”

Illustrious grumbled to herself as she continued patrolling the site.

From above, the city was beginning to take shape. The central area followed a rectangular grid pattern, symmetrically arranged along a central axis. The area spanned over 50,000 square kilometers.

However, due to incomplete resources, most of the buildings were little more than skeletal frames, awaiting further construction.

For now, the shipgirls still lived at the port, so there was no immediate rush.

In the city’s outer agricultural zone, Manjuus drove specially designed tractors to plow the fields.

Thanks to the efforts of Ning Hai and Ping Hai, they had learned basic farming techniques, raising the Starsea Alliance’s agricultural level to the industrial age.

In the distance, designated spaces for airports and starship landing zones were visible.

It was hard not to imagine how magnificent the city would look when fully realized.

...

In the naval base’s top-floor office.

After finishing his daily workload, Setsuna leaned back in his chair and projected the Hyperdimensional Star Map in front of him, observing his neighboring worlds.

During idle moments like this, he enjoyed gazing at the hyperdimensional star map.

There was something surreal about being surrounded by a universe of stars, even if his civilization hadn’t yet reached the space age to witness the real thing.

The same five worlds remained marked on the map: three technological civilizations and two magical ones.

”Hmm…”

”Should I try reaching out to the other worlds?”

With his dimensional portal skill almost off cooldown, Setsuna began to deliberate.

Establishing physical interaction with another world was the only meaningful way to communicate.

Otherwise, like with Muzan before, shouting insults at each other through a holographic screen achieved nothing.

”Honkai? Nasuverse?”

”Does Nasuverse have Gudako?”

”Wait… the Honkai universe is pre-space age, right? So it should be a second-tier civilization…”

As he mulled this over, he noticed that two neighboring worlds, Demon Slayer and Date A Live, had exclamation marks hovering above them.

”What’s this?”

He tapped on one of the icons.

[You have completed the initial task. Multiverse World Mission functionality unlocked.]

A system notification sounded.

[Certain worlds would now periodically generate world missions. Completing these missions would yield special technologies or magic unique to that world as rewards.]

”Huh?”

World missions.

It reminded Setsuna of MMORPGs, where every NPC seemed to have a glowing exclamation mark or question mark hovering over their heads.

Strolling through the main city could easily leave you saddled with 800 different quests.

Fortunately, his current neighbors were limited in number, sparing him the spectacle of a star map littered with icons.

On the bright side, the system seemed user-friendly—missions were optional. He could accept or ignore them at his leisure, unlike those systems that forcibly dumped him into strange worlds with tasks he couldn’t escape.

He first glanced at the mission for the Date A Live world.

[Eliminate the threat of the Spirit of Origin.]

”…”

Yeah, no. Not touching that. Right now, it’s unclear who would eliminate whom.

He moved on to the Demon Slayer world’s mission.

[World Mission: Demon Slayer]

Objective:

1. Eliminate the Twelve Kizuki.

Rewards:

1. Sun/Moon Breathing Techniques.