Crossover Shipgirls: Building a Dimensional Empire from Scratch

The data Grey extracted from her internal database left the loli researchers at the Starbase in awe.

Previously, they could only rely on Setsuna's broad descriptions to determine research directions. For example, if Setsuna mentioned several types of FTL travel—warp drives, hyperspace, wormholes, or jumps—the lolis would analyze the rough principles, then select the method they deemed most feasible for development.

The same went for technologies like gamma lasers, tachyon lances, and jump drives.

They began by researching the theory, proposing hypotheses, sketching designs, and then letting the Bulins build prototypes. The designs would be adjusted based on the practical results.

Grey, however, brought with her over half of Stellaris' tech tree.

These were all spoils of war she had collected, knowingly or unknowingly, during the war with her creator.

To illustrate: previously they were starting from scratch.

Now, it was as if the textbook had been placed right in front of them. All they had to do was study it diligently.

The lolis in charge of tech research were ecstatic.

Day and night, they translated and compiled the documents, classifying and summarizing the strange technologies.

Even if part of the data had been lost, it was still far more convenient than researching from zero.

A few days later, Kayo Senju presented a summary report to Setsuna.

"Onii-chan, the data brought by 'Gray Tempest' covers most of the physics and engineering tech fields."

"The technology used to create a nanobot civilization is extremely advanced. Even by interstellar standards, it ranks among the top."

"Most importantly, within the ship designs she provided, there are not only Titans and Juggernaut-class starships, but even the 'Colossus Project.'"

"Huh?"

Setsuna sat up straight, signaling for the little loli to continue.

"The 'Colossus' is a super warship used to destroy planets in the Stellaris world. It has no conventional armaments and is instead equipped with a single planet-destroying weapon."

"Each type of planet killer has a different effect. The data Grey brought includes four types: World Cracker, Neutron Sweep, Divine Enforcer, and Nanobot Diffuser."

Setsuna was very familiar with these technologies.

The World Cracker used high-energy beams to ignite the planetary core, shattering the entire planet into pieces.

The Neutron Sweep bombarded the planet's surface with high-energy neutron radiation, wiping out all organic life while leaving buildings and infrastructure intact—ideal for planetary occupation.

The Divine Enforcer was a pacifist tool, wrapping the planet in a sublight-speed dark field barrier. No one could leave or enter.

As for the Nanobot Diffuser... Setsuna suspected this was Grey's personal invention.

It used nanobots to convert all organic life on the planet into machines.

"So we can now build actual planet-killer ships?"

Richelieu looked at the documents Kayo Senju handed over, stunned into silence for a moment.

Originally, they'd thought Setsuna had just picked up another wife.

They hadn't expected Grey to directly push the base through a technological leap.

Juggernauts, Colossus, planet-killer weapons...

If they'd relied solely on their own development, it would have taken ages to research them.

Even if some foundational techs were missing, it didn't matter.

A Colossus is a Colossus!! That's a planet-killer ship!!

"Um... it's not just that. I think the 'Colossus' is kind of inefficient. Theoretically, there should even be weapons capable of destroying stars..."

The little loli smacked her lips, then quickly shook her head and patted her cheeks.

"No no, what am I saying?!"

"The Colossus is too bulky! We can try to disassemble its weapon and mount it on conventional starships."

"?!"

She tapped the holographic interface in front of her, and tens of thousands of complex data points scrolled across the screen.

"Normally, charging a Colossus planet-killer weapon consumes an enormous amount of energy, which is why the ship carries no other armaments."

"But if we rely on the power of Wisdom Cubes—which are energy sources themselves—and add supplementary reactors, we can install Colossus weapons on conventional starships."

"Titans and Juggernaut-class ships can both be outfitted with planet-killer weapons."

Hiss—

The shipgirls looked at each other.

"Approved. Begin testing!"

Setsuna slapped the table, exhilarated.

Faced with such a dazzling and overpowered proposal, he couldn't stay calm.

"So that means the Eternal Snowfall could become an ultimate starship with planet-killing capability, able to manufacture and repair ships on demand, and firepower rivaling a space fortress?!"

"Yes."

Kayo Senju nodded.

"I believe this is already approaching the ultimate form of conventional spacecraft."

"To go further would require things like Battle Moons or Celestial-class weapons."

"???"

Setsuna realized the research lolis had picked up some very peculiar knowledge.

"Where did you hear about these things?"

"Grey-sensei mentioned them. She seems quite knowledgeable in this area. She often talks to us about things like 'efficiency' and 'organic purging'..."

The loli scratched her head.

Thanks to her deep knowledge of engineering and physics, and her rich imagination, Grey quickly bonded with the science-loving researchers.

One side represented the pinnacle of technological constructs, the other, a group passionate about scientific inquiry.

It was a perfect match.

Now, Grey had become a teacher in the eyes of the loli researchers.

"..."

Just the thought of the Empire's planet-killing warships being built by little girls gave Setsuna a strange feeling.

"What is this, Paradox war crimes starting from kindergarten?!"

...

The task of researching the new ship class was handed over to the lolis and Grey.

Designing a Juggernaut equipped with a planet-killer weapon from scratch was undoubtedly a complex undertaking.

In the Stellaris universe, even an advanced interstellar civilization would struggle to construct a Juggernaut. The Starsea Empire had only just entered space.

Fortunately, Grey had brought enough reference materials that they only needed to make minor adjustments to existing designs.

Resources were provided by tributary worlds.

As for the most challenging aspect—craftsmanship—millions of specially configured Bulins stood ready.

As long as they had resources and blueprints, the Bulins could fabricate any new hull for Setsuna and the shipgirls.

Inside the Starbase's engineering division,

the loli researchers could be seen every day arguing fiercely over the Juggernaut's design.

"The Juggernaut has to mount the World Cracker!!! It can destroy planets and also fight powerful enemies in interstellar warfare!"

"Neutron Sweep!!! It preserves planetary resources—just wipe out the enemy and take the planet!"

"Listen, we need both!! Install two!! One World Cracker module and one Sweep module!!!"

"Uh, I heard there's also a planet-killer weapon that reduces enemy intelligence to primitive levels. Should we look into that?..."

If someone unaware of the context overheard the loli discussions, they might be scared half to death.

But in truth, they weren't harboring dangerous PDX war criminal thoughts. They were simply analyzing the pros and cons of the weapons from a technical perspective, like proper scientists.

The shipgirls watching would occasionally join in too, choosing their preferred advanced weapons like they were ordering from a menu.

"Looks like the fleet is about to undergo a major upgrade again."

Everyone was full of anticipation.

"This time, we'll become an interstellar fleet of the Stellaris era."

Due to an unexpected discovery by a science vessel, the fleet made a detour and traveled 3,000 light-years away.

They returned with a nanobot and some advanced civilization technologies, stirring quite the buzz at the base.

After handing off the ship upgrade plans to the loli researchers and letting Grey settle in with everyone, that matter was temporarily wrapped up.

Taking advantage of the lull while waiting for the new ship designs, everyone's focus shifted back to the previously interrupted expedition plans.

"Ahem, our next phase of operations is divided into two main objectives."

In the administrative center's grand conference room, Setsuna announced his plan to everyone.

"First, we'll continue exploring our universe. Unmanned science vessels will be dispatched to scout farther star systems and investigate whether alien civilizations exist in other corners of the Milky Way."

"Bulin and Angeloid construction must keep pace as well. We need to begin planetary development in the Solar System as soon as possible."

The fact that there were no Shroud or aliens, and only Grey existed in the Stellaris universe, puzzled Setsuna.

No one was competing for resources here. It was ideal for farming, but large-scale deep-space surveys were needed to uncover further clues.

"Second, we will begin conquest operations on the five new worlds discovered during this 'One-Zero-Zero' cycle."

He cleared his throat.

"My basic strategy is to tackle the five worlds in order of difficulty—from easiest to hardest."

"Kantai Collection and Uma Musume are relatively simple. The Abyssals aren't a real threat, and we can send a detachment fleet to handle the horse girls."

"The most difficult one is the Puella Magi Madoka Magica world. We need to develop a thorough plan and prepare in advance. It'll come last."

"Oh, and if things go smoothly and we manage to recruit the Law of Cycles, we can bring Madoka along for mechanical divinity work in the Honkai world."

On the holographic display, Setsuna outlined the general conquest roadmap.

The Uma Musume world had no combat or real difficulty. The companions could simply bring the horse girls back.

Just like the Nekopara and Girls und Panzer worlds, there was no need for him to go personally.

As for the KanColle world, Setsuna did need to go in person to retrieve the shipgirls—including both the Naval Base shipgirls and the Abyssals.

"Yay! Shipgirls from another world!"

The Azur Lane and Arpeggio shipgirls perked up with interest.

Richelieu distributed briefing materials on the KanColle world.

The general background was simple:

In a world where humanity had lost control of the seas, many monsters called "Abyssal Fleet" emerged from the ocean.

The only ones who could fight them were girls known as "shipgirls," who inherited the souls of surviving warships.

KanColle shipgirls used purely WWII-era weapons—they had no support from Wisdom Cubes or the chaotic idealistic black tech of Azur Lane.

"The enemy seems about equal to a modern navy? Wouldn't we just A-move and win?"

Grey glanced over the Abyssal Fleet's data.

Their combat power was slightly stronger than the shipgirls and their gear consisted of blackened, modded versions of WWII weapons.

Things like Abyssal Hell Dive Bombers and Abyssal Revenge Torpedo Bombers—but no ability to fight in space, let alone match FTL starships.

"Exactly."

"We'll head over, befriend the Naval Base shipgirls, help them wipe out the Abyssals, and then bring the shipgirls back to the port. Mission complete."

Setsuna explained.

"Oh, also—when we encounter Northern Princess and her sisters, go easy on them. Bring back a few Fortress-class Princesses."

For worlds without high-tier gods or strong power levels, there was no need for intricate schemes.

He openly admitted he was there to recruit shipgirls.

Not gonna lie—KanColle's Shoukaku-mama and Shimakaze were top-tier.

Both were once huge names in the doujin world.

And Northern Princess was just adorable.

"Commander, I have a question."

Gudako sent him a private message through her comms device.

"As far as I know, shipgirls tend to have very high affection levels toward their Commander, right?"

"Mhm."

Setsuna nodded.

"There will eventually be shipgirls from three different worlds stationed at the base. Are your kidneys going to survive? Don't get drained dry just from one trip to the naval base."

"..."

Setsuna paused in silence.

"Just kidding. Worst case, I'll have the Eternal Snowfall activate Silver Party Mode—doesn't matter how many people we have."

"And if needed, I'll add another Wisdom Cube. Triple-core drive, sure."

...

After finalizing the KanColle world strategy and expedition team selection, it was already late at night.

The shipgirls returned to port. The Heroic Spirits and Spirits had no interest in these tech-heavy missions and opted out.

Fuu—

"New shipgirls... I'm looking forward to it."

Leaning back in his office chair, Setsuna let out a long breath.

Just imagining the day when he could give a single order and have shipgirls from three different worlds respond in unison was enough to stir his excitement.

Now that was a real Commander.

Every shipgirl is my wife.jpg.

"Yat Sen, notify the Bulins tomorrow. Have them build another naval base at Golden Horn Bay for the KanColle shipgirls."

"I wonder if we'll encounter Warship Girls R shipgirls someday... then we could establish a Multiversal Shipgirl United Empire. Tsk."

He couldn't help imagining being surrounded by a collection of wives from different worlds.

Glorious from Azur Lane, Lexington from Warship Girls R, Shoukaku from KanColle...

It all felt so harmonious.

"Commander, it's clear you really like them."

Yat Sen brought him a warm drink, placing it gently on the table.

"Isn't it normal for a Commander to like shipgirls?"

Setsuna smiled as he pulled Yat Sen into his arms.

She settled onto his lap, her soft body nestled against him, carrying a faint fragrance.

"Always thinking about girls from other worlds... you're so unfaithful..."

"You've been playing with Grey all day recently. And now you're heading off to the KanColle world. It's been a while since you spent time with me."

Yat Sen spoke with a soft pout.

"The situation was special, I didn't expect Grey to be here."

Setsuna gently brushed her hair aside.

Since Grey was new, it was only natural that the Commander should show her around.

As for expeditions... Yat Sen mostly stayed at the base, helping manage the capital while Setsuna was away, so she hadn't accompanied him much lately.

"You're going to charm the other world's shipgirls again, aren't you?"

"Don't forget about me..."

Yat Sen reached up and pinched Setsuna's cheek.

Her Commander was powerful, handsome, and popular with women. That made Yat Sen happy, but also a bit worried.

Worried that one day he might not like her anymore.

"What do you mean?!"

Setsuna swore he treated every harem member equally.

Then he picked up on a faint trace of jealousy in Yat Sen's tone.

"Are you jealous of Grey?!"

"Worried that she's capable, pretty, and always with me lately? Afraid I'll forget my old love for a new one?"

"No!"

Yat Sen denied it, but her face flushed pink.

The nanobot had indeed sparked a sense of crisis among her and several other shipgirls.

Grey's efficiency was off the charts—even Richelieu had to admit defeat. She possessed knowledge none of them had and was indisputably powerful.

At full strength, she alone could sweep across half the galaxy.

Faced with the "Gray Tempest," Yat Sen felt like she was gazing up at a mountain.

"Don't overthink it. You are you—my oath-bound shipgirl, unique and irreplaceable."

Setsuna whispered softly in her ear.

"No matter how strong new companions may be, your place in my heart has never changed."

"After all, it was you who stood by me when we started from nothing."

"Commander..."

Yat Sen paused briefly, touched by his sincerity.

She instinctively leaned into his embrace, quietly listening to the rhythm of their hearts.

"I'll always be with you."

Setsuna gently stroked her long hair, comforting her.

The administrative building was quiet. With tomorrow's expedition ahead, the shipgirls had all gone to prepare.

After a tender moment,

Yat Sen gazed out the window, resting her head on Setsuna's shoulder, and murmured:

"Once you leave for the KanColle world, we won't see each other for a while."

"Mm..."

Setsuna glanced around the office and down at the Yat Sen in his arms.

She wore a light white short blouse and just-translucent black stockings that hinted at what lay beneath, fueling his imagination.

"This is nice. Let's start with dessert."

"Eh?!"

Yat Sen sensed the shift and gasped in surprise.

"Commander, is this really okay?"

"You know, sometimes when Richelieu and I work late, she asks for a little reward."

"Despite appearances, Richelieu's favorite thing is train bento."

Setsuna teased, inching closer.

"You really are..."

Yat Sen, unable to resist her Commander, pouted one more time but didn't object.

Now she finally understood why Richelieu often stayed late in the administrative center, even when there wasn't that much work.

As an oath-bound shipgirl, it seemed work wasn't the only duty she had to handle.

The Dragon Empery shipgirl sighed quietly in her heart.

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