Crossover Shipgirls: Building a Dimensional Empire from Scratch

Time passed swiftly.

For the shipgirls stationed at the space station, the scout star of the Sky People had merely been an amusing diversion—a bit of entertainment to stave off boredom.

After blowing the asteroid apart and hauling back the fragments, they handed everything over to the Engineering Division for reverse-trace analysis.

On the star map, simulations spanning tens of thousands of light-years were already underway, waiting to pinpoint the homeworld of the Sky People. Once located, the fleet would immediately warp there and toss them all into the Synaptic Lathe.

From the dismantled scout star, it was clear that a species relying on such primitive detection tools couldn’t be particularly strong.

At best, they were on par with cosmic pirates—hardly a threat to the Starsea Empire, whose ambition was to conquer the entire universe. Naturally, such a race had to be erased.

”Hm...”

While the Research Division was busy extracting and studying the Power of the Finality, and the Engineering Division was enthusiastically ’opening up’ the Sky People, Setsuna spent his free time focusing on mastering the Herrscher of Reason’s powers—and, well, raising children with Cecilia.

Quite literally. Little Kiana and Sirin were extremely clingy, treating him as their absolute father figure.

”Look, that’s Papa’s ship. Isn’t it amazing~?”

Near the station’s ship dock, Cecilia led the two little ones on a tour.

”Whoa...”

Staring up at the majestic Eternal Snowfall, both Kiana and Sirin stood with their mouths slightly agape, momentarily stunned.

”Can I fly a ship like that someday?”

Little Kiana asked.

”Of course. If you want, I can give you one right now.”

Setsuna replied.

He extended his hand, invoking the power of the Herrscher of Reason.

On the holographic interface before him appeared a complex schematic—the ship’s AI was already analyzing the blueprint.

Shhh—

In the distant void, a small silver-and-lavender spacecraft materialized within seconds.

It was slightly larger than a shuttlecraft, unarmed, and adorably compact.

”A birthday present for both of you.”

Setsuna gently patted Kiana and Sirin on their heads.

”Waaah—!”

The two little girls’ eyes sparkled like stars.

”So cool!!! How did you do that?!”

”I can create most of the things you want.”

Setsuna said with a smile.

The core of the Herrscher of Reason’s power was understanding—only by fully grasping how something worked could he recreate it using Honkai energy.

Unlike Welt Joyce or Welt Yang, who needed years of engineering and mechanical study to master construction principles, Setsuna could take a shortcut. Thanks to the Eternal Snowfall’s onboard AI and their integrated man-ship interface, all he had to do was feed the blueprint into the system. Once the AI understood it—he understood it.

”So amazing...”

Kiana’s eyes were filled with pure admiration.

”If only I could be as strong as Papa someday...”

”You’ll be able to do great things too. The Herrscher of the Void’s control over imaginary space is also powerful.”

Setsuna pinched her cheek lightly.

”Mmm...”

Kiana still didn’t really understand Honkai energy; she just tilted her head, confused, before running off to the ship with Sirin, both giggling loudly.

Operating the craft was simple—it was fully automated. Voice commands were enough for every function.

”Take off!”

Kiana pointed her little hand forward.

Whooom—

A faint blue flame erupted from the ship’s thrusters as it slowly departed from the docking bay, gliding into the starlit void.

”Waaah! Waaah! Waaah—it’s really flying!!”

The two girls shrieked in delight.

”...Aren’t they a bit too young? Letting them pilot a ship already?”

Cecilia gazed up at the two small dots in the sky, concern written all over her face.

”They won’t crash into anything... right?”

”Relax. The Herrscher of Reason has absolute control over anything he creates.”

Setsuna chuckled.

”Besides, piloting lessons start young in the Starsea Empire. You’ve seen the little shipgirls in the dockyard—barely born, and already transforming into battleships to roam the solar system. With a few upgrades, a few hundred or thousand light-years would be nothing.”

”This isn’t the same at all! They’re not even the same species!”

Cecilia lightly smacked Setsuna’s arm.

”Oh, oh, oh, oh, oh—”

Kiana and Sirin had been exploring the solar system for quite a while before finally returning under Setsuna’s orders, still reluctant to leave.

”Papa, I want to fly a big ship! One just like that!”

Kiana tugged at Setsuna’s sleeve, pointing at a distant battleship.

”When you grow up.”

Setsuna flicked the white-haired girl’s forehead and gestured for Cecilia to take them both to eat.

He then went back to studying his Herrscher of Reason powers.

”So basically... if it’s something I can understand, I can create it...”

”Doesn’t that mean I can remodel my own ship body?”

He projected the Eternal Snowfall into view.

[Structural Design Analysis Loading...]

A complex schematic appeared across the holographic interface.

Modifying other people’s ships or starships was difficult—but as the Juggernaut was an extension of himself, he understood every part of it completely.

Every bolt, every corner, every component aboard it—he knew them all inside and out.

Shhh—

Setsuna first attempted a small-scale modification.

A turret detached from the ship’s weapon wing. Using the Herrscher of Reason’s power, he reshaped it into a much larger axial cannon.

”Hmm...”

He closed his eyes and felt the results. It worked, but it looked... off—awkwardly mismatched.

He reshaped the weapon again, this time making it stylistically consistent with the surrounding armaments.

Then, he began to consider what else he could add to the ship.

From the start, the Eternal Snowfall had been designed with plenty of redundant space for future upgrades and modifications.

Most weapons could be constructed directly from the database’s schematics. Once attached to the hull, he could instantly tell whether they worked or not.

If anything malfunctioned, he would sense it within seconds.

”Maybe add another hangar? More carrier aircraft? Or...”

Upgrading his own ship body was unexpectedly entertaining. As he brainstormed, something came to mind—

The Transdimensional Starship.

Back then, time had been short and resources limited, so only a prototype battleship had been built as a test subject.

His own Juggernaut body had never undergone transdimensional enhancement.

He didn’t fully understand dimensional science—but that didn’t matter. The ship’s AI did. The Transdimensional Starship was part of him anyway.

Beep—

Setsuna opened a channel to Siren-chan.

”Send me the data on the Transdimensional Starship.”

”Eh?... Did something malfunction? We can come over for repairs, just a second—”

The wide-eyed Siren girl panicked, worried that the ship might’ve glitched and sent Setsuna spiraling into some alternate dimension.

”No, I’m trying to understand and recreate it using the Herrscher of Reason’s power.”

”Ah—ah—ah—?! You’re what?!”

Terrified but obedient, the Siren girl transmitted a sea of data to him.

Setsuna didn’t understand a single equation, so he dumped everything into the onboard computer.

Vrrr—

With AI assistance, countless dazzling images and incomprehensible formulas flashed before his eyes—design schematics so advanced they defied reason itself.

Even for a super-AI, parsing what had taken the Sirens years to construct was no simple task.

Then, following instinct and computational output, he extended his hand and invoked his power.

Shhh—

He felt a surge of energy being drained from him—the more advanced and complex the structure, the more power the Herrscher of Reason consumed.

Inside the Juggernaut’s drive chamber, a strange engine materialized out of thin air.

Its design resembled a Klein bottle—interwoven and self-connected, an impossibility for any three-dimensional object.

Using his authority, he linked the transdimensional engine to the ship’s power module, making it part of the Eternal Snowfall.

”Whew—”

He exhaled, rubbing his temples as his mind filled with bizarre and intricate knowledge.

Boom—

With a thought, the Eternal Snowfall’s entire form began to twist and shift.

Its sharp lines softened, its bridge merged seamlessly into its hull.

The Juggernaut, already planetary in scale, saw its massive weapon wings extend outward at impossible angles, expanding severalfold.

From a distance, its dark blue-black wings seemed to divide the solar system itself, like a cosmic eagle spreading its wings across the void—its sheer size defied comprehension.

No detection system could analyze it; every sensor returned errors in chaos.

On the space station, the Research Division girls panicked, fearing something had gone wrong with the Commander.

”High-dimensional expansion?!”

Grey reacted first, staring in disbelief.

Such a violation of physical law could only mean one thing—it had transcended dimensions.

Just like the first time they’d seen the Transdimensional Starship, what they were witnessing now was merely the Eternal Snowfall’s three-dimensional projection.

”Yes, I’m attempting to use the Herrscher of Reason’s power to perform a transdimensional upgrade.”

Setsuna clicked his tongue.

”But right now, I’ve only managed to ’craft’ the engine. The rest of the hull has compatibility issues—it’s a bit buggy. I’ll need more time for full integration.”

”...”

The nanobot was stunned.

”Perfect! Commander, this makes future upgrades to your ship body so much easier!”

”If we just give you the blueprints, you can handle the upgrades yourself! Not only will it save us a ton of Bulins, but even the materials too!”

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