Crossover Shipgirls: Building a Dimensional Empire from Scratch

Throughout history, the management of tributary states or colonies has largely followed two approaches.

One is the brute-force method akin to the adventurers of the Age of Exploration, who carried out reckless exploitation, stripping regions of every resource before leaving them desolate. Such methods were excessively harsh, uncivilized, and unsustainable.

As the colonial era unfolded, industrial nations like Britain and France adopted relatively gentler methods of conquest over agricultural societies. They ensured the local population could sustain themselves while extracting minerals, spices, food, and other resources. This reduced resistance, enabling both sides to coexist—albeit unequally.

Setsuna’s approach, however, aimed even further.

”Ning Hai, Ping Hai, aside from managing agriculture here, you’ll also take on the responsibility of overseeing the affairs in the Demon Slayer world.”

”I’ll lay out the development plans for that world—just follow them,” he said, spreading a world map on the table.

”First, we’ll need to improve their technological standards. At the very least, the entire world must rapidly enter the industrial era, especially the underdeveloped agricultural nations in Asia and Africa—they’re far too backward.”

”Then, we’ll manufacture tractors, harvesters, and other agricultural machinery to distribute to them. Teach their farmers modernized production methods. Fertilizers? The industrialized nations can spare some for now.”

”We’ll construct railroads, creating networks connecting industrial hubs in each country.”

”Electricity is vital as well. If necessary, send out the Bulin-class ships to help build power grids. For them, this kind of work is simple and won’t take much effort.”

”Additionally, public health is crucial. Teach them to boil water, and ask the dockyards to mass-produce penicillin and malaria vaccines for distribution.”

”???”

Ning Hai and Ping Hai were completely dumbfounded.

”Commander, are you doing charity work? I thought you went there to plunder!”

To them, this sounded more like comprehensive aid for infrastructure development than any kind of resource exploitation. It was a stark contrast to the fleet’s recent escapades—thrashing every nation into submission and forcing them into subservience.

”Beating them into submission was just to establish authority,” Setsuna explained with a smile. ”If they’re grudgingly cooperative, they might secretly cause trouble later.”

”You can’t manage an entire world solely through brute force.”

”And let me reiterate, our goal in the Demon Slayer world is sustainable development.”

In the early 20th century, the technological disparities across Earth were immense. Advanced nations like Britain, America, and France had already completed industrialization. Others, such as Japan and Russia, teetered between agrarian and industrial economies. Meanwhile, large parts of Asia, Africa, and Latin America remained underdeveloped agricultural regions or even primitive tribal societies.

It was impossible to extract much value from such underdeveloped territories.

So why not help them industrialize? With improved productivity in agriculture and industry, they could yield more, and Setsuna could extract greater resources from them.

It was like baking a larger cake—everyone would get a bigger slice.

With higher living standards, ordinary people wouldn’t resent the overlord state. Instead, they’d be grateful, thankful to the invaders who brought them electricity, penicillin, and fertilizers.

Eventually, the Demon Slayer world could become a stable logistical base for Setsuna’s civilization—a win-win situation. Perhaps even a win-win-win, depending on how you looked at it.

This plan was leagues ahead of the traditional exploitative colonial systems.

”Wow, this is so complicated…”

”We’ll have to take our time studying this…” Ning Hai and Ping Hai left with a stack of detailed plans, their heads spinning.

After arranging for the Demon Slayer world’s future, Setsuna checked on the progress made in the port and homeworld during his month-long absence.

The capital city was more than halfway constructed. The industrial zone was operational, and the residential and administrative districts were fully developed. However, with a population of fewer than 600—including newly arrived Bulins and Manjuus—it felt overly spacious in a city spanning 50,000 square kilometers.

Even the little yellow chickens each had their own duplex apartment, though they still preferred the nests they built themselves.

At the port, shipgirls continued their relentless weapon experiments, regularly sending out flying squadrons to clear nearby sea routes and harass Sirens.

With Siren battleships unable to target the skies effectively and their anti-aircraft guns proving ineffective, the port’s operational radius had expanded considerably.

Moreover, the shipgirls were researching even more advanced and portable weapons, particularly those capable of combating high-level Sirens.

Overall, progress was going smoothly. With the Demon Slayer world soon contributing resources, Setsuna anticipated the arrival of the space age before long.

”Where’s my Gundam?”

Suddenly remembering something, Setsuna perked up. Before he’d left for the Demon Slayer world, Akashi had been working on a Gundam project. With the advent of rocket-propelled shipgirls, he wondered how far the project had progressed.

He quickly made his way to Akashi’s workshop.

Bang! Bang! Bang!

Inside, the sound of hammering echoed loudly.

”Hey, Akashi?” Setsuna knocked on the door.

”Commander! Welcome home, meow!” The cat-like ears shipgirl swung the door open with a wide grin.

”Come in! Choose your deployment mech—and don’t forget to pay for it, meow!”

Akashi’s workshop was massive—more accurately, it was practically a factory.

Equipped with lathes, cranes, and furnaces, it had everything one might need. Dozens of Bulins bustled about inside, wielding tools and hammering away. As the port’s dedicated repair ship, Akashi’s usual ”experiments” involved servicing or modifying shipgirls that weighed tens of thousands of tons.

The first thing Setsuna noticed upon entering was a lineup of Gundams standing against the wall.

Arranged by height from left to right, there were nine in total.

The leftmost one was a dusty yellow, appearing somewhat primitive, standing roughly 17 or 18 meters tall. It was clearly a mass-produced grunt model. The ones on the right, however, had entirely different aesthetics—sleek lines, intricate equipment, and an unmistakable sense of power.

”You built this many?!” Setsuna was stunned.

”Tech development needs to proceed step by step, meow. Without building the basic models and understanding their principles, I wouldn’t be able to construct the more advanced ones!” Akashi explained with pride, guiding Setsuna to admire her creations.

”So, I built everything—from the simplest models to the high-end versions. Any Gundam we’re capable of making, you can pilot, meow!”

She pointed to the leftmost model.

”That’s the Zaku Prototype Unit. About 50 tons, equipped with a saber and two machine guns.”

”Next is the Zaku II model—better mobility, stronger armor, and larger-caliber machine guns.”

”But those are all mass-production models, meow. You wouldn’t want those…”

Up close, the mechas were colossal. Neither Setsuna nor Akashi could even reach their knees.

Considering how many units Akashi had produced in just over a month, it was clear the Bulins had been tirelessly efficient, and Akashi herself had poured her heart into the project.

”Thanks.” Setsuna smiled, ruffling Akashi’s head and giving her cat-like ears a playful rub.

”Mmm! Commander! Listen to my introduction properly, meow!” Akashi’s face flushed as her ears twitched. ”Teasing your head engineer won’t get you discounts, meow!”

They continued moving down the line.

”Now we’re entering the realm of hero units!”

Akashi stopped in front of a blue-and-white Gundam wielding a massive hammer-spear.

”ASW-G-08, Barbatos.”

”According to the manual, it was piloted by someone named Mikazuki Augus, meow.”

”This Gundam excels in close combat and boasts impressive mobility!”

Setsuna looked up at Barbatos. Piloting a Gundam to beat enemies with a hammer-spear certainly carried a violent aesthetic appeal.

With its raw power, this model could probably crush a warship with a single blow. However, Setsuna felt it didn’t suit him. After devouring the Wisdom Cube, his physical capabilities were already formidable; what he lacked was long-range firepower.

”RX-0, Unicorn.”

Beside Barbatos stood a sleek, white Gundam with a striking horn on its head, slightly larger than Barbatos.

”This unit can activate Destroy Mode, meow!” Akashi exclaimed excitedly. ”Once activated, it deploys a psychoframe field to deflect standard ranged attacks and controls remote weapons, meow!”

”The pilot was… Banagher Links?”

”N-T-D, huh… I’m tempted to pilot the Unicorn…” Setsuna stroked his chin, scrutinizing the machine.

”So, is this the one?”

”Wait, meow! What if I said there’s another Unicorn? You could take the shipgirl Unicorn aboard the Gundam Unicorn and pilot it together, meow…”

”???”

Akashi confused herself with her own words.

Next was another classic unit. Its white-and-blue body and the eight weaponized wings unfurled behind it gave it an angelic silhouette. The Gundam was instantly recognizable.

”Strike Freedom, piloted by Kira Yamato.”

”Powered by a deuterion reactor—kind of like nuclear fusion but not exactly the same. Gundam tech is really weird, meow…”

”Its torso houses the MGX-2235 Multi-Phase Beam Cannon. Our experiments at the port showed it could penetrate high-tier Siren defenses, meow.”

”It also has a beam saber and shield. Honestly, I don’t get why Gundams need melee weapons, but since they were on the design plans, I built them anyway…”

Akashi muttered to herself as she continued introducing the units.

”Additionally, we have the Gundam Exia and Infinite Justice…”

”All the Gundams we could replicate are here, except for a few overly complex ones I’m still researching, meow.”

”Commander, which one do you want to pilot?”

Apart from the three grunt models, Akashi had successfully recreated six protagonist-tier Gundams. Their performance and designs perfectly replicated the originals.

These units required their pilots to have exceptional physical and mental fortitude. However, thanks to the enhancements from the Wisdom Cube, that wasn’t a problem.

”Can I swap out the Gundam’s equipment later?” Setsuna suddenly asked. While these iconic Gundams were impressive, their loadouts were tailored for their original pilots. He wanted a Gundam uniquely suited to himself.

”Of course, meow! All the equipment on these Gundams is modular and interchangeable, meow. If you want, I can even attach battleship cannons to them!”

”However, I’d suggest getting familiar with piloting one first before customizing anything, meow.”

”Fair enough. I’ll try this one first.” Setsuna thought for a moment before choosing the Strike Freedom.

Climbing up a ladder, he entered the cockpit.

Click.

Seated comfortably, he was greeted by a colorful array of holographic controls. Despite being his first time piloting a Gundam, he instinctively understood the controls as if he had done it before.

”Is this because I can integrate abilities from other worlds? Not bad.”

”Let’s take off.”

The hangar’s dome slowly opened, revealing the sky above the naval base.

Boom!

On the shoreline, shipgirls and Bulins paused their activities, astonished as a Gundam launched into the sky, trailing flames.

The shipgirls flying nearby were particularly startled.

”Commander! The Commander is piloting a Gundam into the sky!”

”Commander, take me with you! I want to pilot a Gundam too!”