Crossover Shipgirls: Building a Dimensional Empire from Scratch

Late at night.

The starship floated quietly in the boundless void.

A nanomachine girl with long ash-gray hair sat atop the bridge, her legs dangling freely as she idly swung them back and forth.

Her gaze, carrying a hint of depth, wandered toward the distant stars.

”Heh heh heh...”

Her mood seemed rather good as she hummed a tune stored deep within her memory—a melody so ancient that she had long forgotten how many epochs it had endured.

The lyrics’ language had been lost to time, and even before she had become the Gray Tempest that swept through star clusters, this song had already existed.

Tens of millions, even hundreds of millions of years of history meant little to the universe or to an eternal artificial intelligence like her.

”Truly wonderful—”

Grey felt that having the chance to come to the Milky Way was absolutely amazing.

No—more precisely, following Setsuna through countless universes was infinitely better than rotting away in the L-cluster, waiting for death.

It had been one thrilling adventure after another.

”How long did I swear loyalty to the Commander for again? Two thousand years? Five thousand? Huh... thinking back to when we first met, that term was probably way too short.”

”I’ll have to notify him when I get the chance—let’s make it permanent this time, hmm.”

The nanomachine girl decided that a sense of ceremony was still important—after all, logic was everything to an artificial being.

From the top of the bridge’s weapon tower, she leapt down lightly, landing gracefully on the deck.

Step by step, she began measuring the vast Imperial flagship beneath her feet.

By instinct, she was fascinated by advanced mechanical creations.

”Hmm?”

After only a few steps, she suddenly froze.

From a nearby cabin came the faint sound of soft, trembling cries.

At first, she thought someone had been wronged—perhaps sitting alone in sadness.

But the closer she got, the stranger the sounds became.

Curiosity got the better of her.

Running along the ship’s outer wall, she moved like a shadow—her nanomachine body letting her traverse the nearly vertical surface with ease.

”Ha! Found it!”

With a swift motion, she peeked through the panoramic window.

And then—she saw two enormous ’righteous forces’ pressing right against the glass.

”Commander, isn’t this... not a good spot? Shouldn’t we go back to the bedroom?”

Saint Louis leaned bonelessly against Setsuna, her long blue hair cascading down one side. Her misty eyes carried both intoxication and allure.

Her fingers gently traced across his cheek.

—Shipgirls usually couldn’t get drunk. Grey was sure of it.

After being modified into starship-class beings, even if they downed the entire stock of a brewery, they’d be perfectly fine.

So, clearly, this was just a pretense... for something else entirely.

”It’s fine. The Eternal Snowfall is in a time-distorted state—no one outside can observe what’s happening within.”

Setsuna said calmly.

”Only the ship’s crew could see us, and this is the top deck. In the middle of the night, who’d be bored enough to wander out here?”

”Hmm... that’s true...”

Saint Louis leaned against the window, bracing herself with one hand.

”Still... maybe we should pull the curtains...”

As she lowered her head, her gaze met that of the nanomachine girl outside.

Both froze in shock.

”Ah?”

”Wha—?!”

Saint Louis let out a startled gasp.

Whoosh—

Setsuna reached out, pulling Grey inside with imaginary energy, and gave her two firm knocks on the head.

”What are you doing here? Sneaking around in the middle of the night to spy on me?”

”I’m a nanomachine robot—I don’t need sleep!”

Grey grumbled, clutching her head.

”I was just passing by!!!”

”Huh?”

Setsuna sighed. Only she would wander around aimlessly at this hour.

”Go on—don’t make this a habit.”

Just as he was about to send her off—

Grey puffed her cheeks and leaned closer.

”Commander, I’ve had enough! You never invite me to your parties!”

”I protest! I demand to join your party right now!”

”???”

Saint Louis blinked, puzzled.

”Um... I don’t quite understand. Aren’t you made up of countless nanomachines, like a gray storm? How are you supposed to...?”

She couldn’t imagine how Grey—an entire collective civilization—was supposed to literally ”join a party.”

”I can simulate anything down to the molecular level. Not even a single cell would be wrong.”

Grey patted her chest proudly, gray mist spreading from her body as her figure blurred.

A few seconds later, a shipgirl identical to Saint Louis stood before Setsuna.

Their appearances, expressions, and even their clothes were indistinguishable—accurate down to each strand of hair and every stitch in the fabric.

”Commander, how about this? Do you like it?”

Wearing Saint Louis’s face, Grey smiled at him.

”?”

Saint Louis instantly froze, expression stiff.

”Or I can take another form.”

”According to my statistical records, in the past thirty days, the one you’ve shared a bed with most frequently is... Taihou?”

Whoosh—

Her figure shimmered again, transforming into the voluptuous black-haired, red-eyed Sakura Empire carrier.

”How about this? Perfect, right?”

”Whoever you want me to be, I can become them—even an ancient god, if you wish! Well, though their complexity is a bit troublesome...”

”...”

Setsuna’s face darkened.

Honestly speaking, he preferred Grey’s original appearance. A nanomachine was a nanomachine—there was no need to imitate others.

”Change back. Parties are under real-name registration—strictly no impersonation of others.”

...

Time flowed, and life aboard the Eternal Snowfall passed in the blink of an eye.

After simulating hundreds of day-night cycles under the holographic dome, the starship trembled slightly as it disengaged from the spacetime distortion.

On Earth, in the capital city, the first rays of sunlight were just now rising over the ocean horizon, spreading evenly across the city.

At school, the little lolis rubbed their eyes, washed up, and prepared for class.

At the port, the Bulins also began to stir.

”Eh, the Commander’s really amazing.”

The Research Division girls, the Angeloids, and the academy lolis all sighed in admiration.

”He manages such a huge nation, handles tons of work every day, and still goes on interdimensional expeditions from time to time.”

”And every time he comes back, he only rests for one night... We should really learn from him!”

”Yeahhh!!!”

The clueless little ones cheered in unison.

”...”

Kayo Senju, Midori Fuse, and the others who often boarded the Eternal Snowfall exchanged awkward glances.

They had no idea how to explain things to the girls.

On second thought... maybe it was better if they didn’t. They’d understand one day. Probably.

”Ugh... I didn’t get any time alone with Onii-chan again...”

A few of the little girls pouted in disappointment.

”There were way too many shipgirls this time! The Eternal Snowfall was full of them—always crowding around Onii-chan, hmph...”

The shipgirls treated them like daughters, and Setsuna treated them the same way.

But... some of the little ones had started developing peculiar ideas.

”Isn’t there a way to grow up faster? Life Sciences Division? I want to be like Taihou or Illustrious...”

The suggestive tone made Kayo Senju twitch nervously.

”Don’t even think about growing up too fast! Just wait—you’ll get your chance one day, alright?!”

...

Elsewhere.

”Phew—”

The shipgirls had all returned to the port.

”Tch, just some Tiger Vanguard...”

Long Island jumped off her couch-bed energetically, grabbing a soda and chugging it down.

”Zzz... zzz...”

Beside her, a white-haired, red-eyed, twin-tailed destroyer swayed sleepily, resting her chin on her palm.

”You gamed all night again... huh? Anchorage and the others are back.”

She turned her head—then froze.

Something about them felt... different.

Each of them carried a soft, glowing charm in their eyes.

Shipgirls were already naturally beautiful—flawless even without makeup or effort. But after spending a night aboard the Eternal Snowfall, they exuded a different aura altogether.

It was... mature. Like wives.

Anchorage, usually cheerful and innocent, now seemed calmer—on her left ring finger shimmered a delicate silver ring.

Saint Louis, on the other hand, was adjusting her hair while muttering softly.

”The Commander really... went through so many of my outfits. I really liked that gown too... Ah well, I’ll just ask the Bulins to make me a few more later...”

”???”

Long Island felt like she had missed something monumental.

”You all just went up for dinner, right? Just one night, right?”

”...”

Saint Louis smiled without answering.

”The Commander really was just hosting a victory banquet, right?”

Anchorage silently pulled a small gift box from her bag—the one Setsuna had given her.

”...If only someday, I could have a little shipgirl with the Commander... a little Anchorage, hmm...”

”Ah?!”

The shipgirls who had stayed behind in the port all slapped their foreheads.

Oh no.

They’d fallen behind.

...

”Mm...”

Administrative Center.

Setsuna yawned and sank back into his chair.

His waist ached a little.

Even though he had fused with the META Cube, the Allspark, and the Cocoon of Finality—his physical endurance was incredible, but even that had limits.

After all, dealing with a horde of passionate shipgirls, along with the ever-clingy Spirits, Heroic Spirits, ordinary girls, ancient gods, and dragons—it was a life of exhaustion and bliss.

Now, finally entering true ”sage mode,” he could afford to think about other matters.

Whoosh—

A holographic interface unfolded before his eyes. He first reviewed the current state of cosmic expansion and the progress of various subordinate worlds.

”Dyson Swarm construction progress: 23%. Matter Decompressor completion: 19%. Estimated duration...”

”The Horizon Needle’s framework is complete—preparing for preliminary experiments...”

Across the galaxy, the Bulins and Angeloids were working tirelessly on megastructure projects.

Around the Solar System’s Starbase, countless construction platforms were operating in orbit—turning humanity’s infrastructure obsession into an interstellar reality.

”The Horizon Needle’s progressing that fast?”

”Three-seven-seven,” he muttered, noticing that compared to other megastructures, this one—the stellar-scale ascension construct for Cosmogenesis—was advancing the quickest.

”Yes,” Grey replied, nodding. ”Probably because we’ve previously studied technologies related to altering universal laws. The concept isn’t too hard for the Research Division to grasp.”

”Though the Zero-Homer’s data was somewhat simplified, it still works as a theoretical foundation.”

”In the Three-Body Problem universe, even god-level civilizations still rely on external law-based weapons like the Dual-Vector Foil.”

”They believed it was impossible to directly modify universal constants—but with the Horizon Needle, we can actually do it.”

In the early eras of the Stellar Age, weapons were still bound by energy and kinetic principles.

But after the creation of Ascension megastructures, everything changed.

”Hmm... currently, the Research Division is developing several methods to manipulate fundamental laws. They’ll soon enter the testing phase.”

As she spoke, she transmitted the data directly to Setsuna.

”For example—modifying the value of pi. What if we rounded it off? Doesn’t 3.1415 feel a bit inelegant and hard to remember? Making it 3.0 or 4.0 would be so much more fun.”

”Of course, we’re still simulating what kind of catastrophes might occur if we changed the entire universe’s value of pi.”

”Other concepts include altering visible light wavelengths, increasing or decreasing the speed of light in a vacuum—yes, just like what the Three-Body Problem world imagined. An almost infinite light speed—we can now replicate that using the Horizon Needle.”

A flood of absurd theories left the shipgirls and others stunned into silence.

”If we rounded off the universal pi... what would happen?”

Formidable tried to imagine her turrets turning into polygonal shapes, as if she’d stepped into a Minecraft world.

Even with her imagination stretched to its limits, it was impossible to picture what a universe with pi equal to 3—or 4—would even look like.

”We’ll just test it in some unlucky universe later. Definitely not in our own,” the nanomachine girl muttered.

Human Evil nodded solemnly in agreement.

”...Alright, tell the Research Division to keep it up. Whatever resources they need, they’ll have.”

Setsuna reviewed a few of the requests from various departments—mostly for permission to conduct experiments in certain star systems, or to send extra Bulins and Angeloids for assistance, or occasionally, to carry out testing in another universe.

He approved two or three requests with a flick of his hand.

As for the subordinate worlds, Sophon—serving as their supreme administrator—maintained 24/7 real-time surveillance over all twenty-plus universes.

Every minute event could be instantly transmitted to Sophon Unit 1 in the capital.

Everything was stable—progressing smoothly and in perfect order.

Whoosh—

He opened the hyperdimensional star map before him.

Perhaps it was time to expand the borders again—or maybe... plan the next conquest across worlds.

”Hmm...”

On the star map, five targets remained: No Game No Life, Puella Magi Madoka Magica, A Certain Magical Index, Mondaiji, and Gurren Lagann.

”Oh? Another chance to go knock some heads? Commander, what’s the plan?”

Human Evil and Grey leaned in curiously.

”Start with the weakest.”

When it came to conquering worlds, Setsuna followed a simple philosophy—start small. Gather resources from weaker universes, then use the accumulated strength to take on stronger ones.

—Except for Nyarlathotep, of course. The Cthulhu girls were all model citizens by comparison. No need for war—Starsea Empire’s cultural exports alone were enough to win them over.

”In that case, it’ll be easy.”

Grey accessed the vast interdimensional database and pulled up information on the No Game No Life universe, quickly reviewing its settings.

”There sure are a lot of races there. Old Deus, Flügel, Werebeasts... oh, and the Werebeasts have tons of cute beast-ear girls, don’t they? Way easier on the eyes than in most fantasy worlds.”

”Tch, the list goes on and on...”

As they were planning—

Beep—

A message popped up, and a communication window opened before them.

”Good day, Mr. Setsuna. Are you available right now?”

”I heard you recently went on another interdimensional expedition?”

Leonardo da Vinci’s familiar face appeared on the screen.

She had meant to casually check in on his status, but upon seeing him surrounded by shipgirls and maids—pink and blue ones at that—she immediately realized he was doing more than fine.

”Oh? You guys? Long time no see.”

Setsuna smiled and pulled Gudako closer, exchanging a few greetings with Da Vinci and Dr. Romani.

”Found another Singularity?”

”Yes.”

Da Vinci nodded.

”This one took a bit longer to locate. Chaldeas keeps malfunctioning lately... sorry to bother you again.”

”At this point, Chaldea still doesn’t have the means to resolve Singularities independently. My apologies...”

At first, it had seemed like they were both doomed worlds working together to rebuild humanity.

But while Setsuna had already gone galactic and founded an interstellar empire, Chaldea was... still struggling to stay afloat.

”No problem. I said I’d help restore Human Order, and I intend to keep that promise.”

Setsuna tapped the desk lightly.

Whoosh—

Chaldea’s mission data was transmitted through the network.

”Let’s see... the sixth Singularity, dated AD 1273.”

Dr. Romani cleared his throat.

”The Sixth Singularity: The Holy Round Table Domain—Camelot.”

Setsuna was familiar with it.

This Singularity featured another version of the ahoge king—the Lion King.

In that timeline, Artoria Pendragon had survived past her destined death due to Bedivere’s failure to return Excalibur. Cursed by immortality, she became a wandering spirit bound to the divine weapon Rhongomyniad.

Over time, the holy lance’s divine essence eroded her humanity, transforming her into the Goddess Rhongomyniad.

In the Sixth Singularity, she summoned her Round Table Knights, repelled the Crusaders, and used the holy lance to recreate the Holy City.

She divided the land with the Sun King and the Mountain People, forming three competing powers, declaring herself the Lion King.

The Lion King represented Artoria’s fully deified state—more mature, more resolute, but utterly devoid of human warmth.

”Interesting... so I can start collecting Ahoge Kings now?”

Setsuna mused aloud. The Type-Moon world was famous for its endless variants of the same Heroic Spirits. Like Jeanne d’Arc and Jeanne Alter, or Nero and Bride Nero—Artoria was the ultimate example.

Saber Artoria, Lancer Artoria, Rider Artoria, Alter, Caster Artoria, Lily Artoria...

At this rate, he could form a full Ahoge Legion.

”Another me, huh? Master, I’d like to see what I could have become. She became a king? Do you think she’s... a good version of me?”

The current Artoria stopped munching her snack and looked at him seriously.

”She’s much harsher than you.”

Setsuna ruffled her hair with a grin.

He couldn’t help but look forward to a duel between the two kings—Artoria vs. Lion King.

Beside them, Gudako suddenly turned to Mordred, patting her shoulder.

”Hey, Mo—soon, the capital’s going to be filled with your fathers.”

”There’s the sword one, the lance one, the little Lily one... you’d better keep the family tree straight.”

”Huh?!”

Mordred nearly choked.

What the hell—was her Master going around collecting more dads?!

Different timelines, different versions... all kinds of fathers?

She already had a complicated relationship with Artoria. If it weren’t for the capital’s strict laws—and Setsuna’s constant interference—she’d probably challenge her ”glorious father” to a duel every day.

But if he actually gathered multiple Artorias from various Singularities and Lostbelts...

Mordred covered her face.

Ah, her brain hurt.

—

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