Crossover Shipgirls: Building a Dimensional Empire from Scratch

After sending off the Natural Selection and Blue Space, Setsuna focused on constructing the Trisolaran world outpost and researching this universe’s technologies.

The shipgirls split into several fleets, using the Solar System as their center, to scout and eliminate nearby alien civilizations and fleets.

Their goal was to carve out a 200-light-year security zone around the starbase.

The loli researchers aboard, along with the two Sirens who had tagged along out of curiosity, turned their attention toward the spoils of war captured from this universe.

At the research building beside the starbase—

Although much smaller in scale than the main world base, it was still fully equipped with experimental devices.

Most of the Trisolaran world’s technology lay in physics and engineering. Accordingly, most of the loli researchers assigned here were from those two departments.

”Mm, Commander, we’ve studied the captured Trisolaran starships, technologies, and detectors.”

After several days of work, Kayo Senju reported her findings to Setsuna.

”Their overall technological level isn’t high. Their space warships are entirely inferior to ours, without any reference value.”

”The Droplet as a detector isn’t advanced either. We already have sensors capable of real-time monitoring within a range of dozens of light-years—there’s no need for such sub-light-speed devices.”

”As for the strong interaction material composing it, we can manufacture that too. But I think it’s inferior to the zero-element nanocomposite armor we use on starships.”

Setsuna wasn’t surprised. The current starships had been built by Grey using the Creator’s legacy technology, mixed with Siren modifications.

They stood at the pinnacle of the stellar worlds, naturally far beyond sub-light natives.

”However, we did discover something else of interest.”

The little loli projected a heap of complex data onto the holographic display.

”The sophon.”

”It’s an intelligent microscopic particle, involving dimensional technology. Both its functions and its construction are fascinating.”

The Trisolarans had once used sophons to interfere with physics experiments on Earth for 200 years, sealing humanity’s scientific progress.

Sophons could also draw energy from the vacuum, travel at near-light speed, and use quantum entanglement for real-time communication.

By switching dimensions, they could access any location through higher-dimensional space. In theory, nothing could escape sophon surveillance.

Otherwise, humanity would never have resorted to the Wallfacer Plan to counter the Trisolarans.

”Can we make some?”

Setsuna asked.

”Technically, it’s not difficult, but we currently lack the equipment. We’d need a specially-built giant particle accelerator, along with tools for two-dimensional etching.”

Kayo Senju answered.

”Whatever you need, have the Bulin build it when we return.”

Setsuna decided firmly.

Sophons were also multifunctional artificial intelligences, with extremely powerful data analysis abilities.

One day, they could even be made into humanoid forms to assist with his work.

”Well… if we need one urgently, we could actually pick up a ready-made one.”

Kayo Senju pointed toward Earth.

”The Trisolarans had launched a sophon there before. After their homeworld and First Fleet were destroyed, the sophon lost its controller and is now ownerless.”

”With some effort, we could seize control of it.”

”Oh?”

Setsuna became intrigued.

Using the starship’s sensors and scanners, they could pinpoint the sophon’s exact location.

At its core, it was a fundamental particle, currently maintaining a three-dimensional form, hovering in outer space.

”Do it.”

At the order, aboard the Eternal Snowfall, Nymph and the loli researchers initiated a signal intrusion into the sophon.

”Mm, Master, I’ve never hacked into something the size of a particle before. I’ll give it a try.”

Nymph scratched her head.

Sitting at the main console, she locked onto the sophon’s position.

As a universal electronic warfare humanoid, she possessed immensely powerful hacking abilities. Having been upgraded multiple times by Daedalus, Grey, and the loli researchers, she now embodied the most advanced information warfare technologies of Synapse and the stellar worlds

One had once been a Fallen Empire, a divine-level civilization of immense glory. The other was a father civilization whose starting point surpassed lightspeed.

No matter how developed Trisolaran computing was, it could never compete against the creations of two such advanced civilizations simultaneously.

Before Nymph’s eyes flashed tens of billions of data streams.

The loli researchers assisted her on the holographic computers.

”Mm, Master, I need to seize control of it first—make the sophon unfold into two dimensions—then rewrite its control instructions…”

Nymph’s eyes turned crimson, countless streams of complex data flickering within.

In outer space, the sophon transformed into a two-dimensional geometric plane of nearly infinite area and zero thickness.

Under planetary gravity, it spread across Earth.

People on the planet looked up and saw the night sky turn into a giant mirror, reflecting everything on Earth clearly.

Continents, oceans, even the image of every individual—all reflected in the heavens.

”What is this?! …”

At first, the crowds were confused.

Soon, some scholars familiar with Trisolaran civilization cried out.

”It’s the sophon!!!”

”This is sophon two-dimensional unfolding!!!”

”???”

”WTF??! Weren’t the Trisolarans completely wiped out?!”

Like triggering collective PTSD, Earth erupted into chaos again, nearly descending into riots.

After the war against the Trisolarans, most had put the sophons out of their minds, assuming they had vanished along with their masters.

No one imagined the thing would resurface.

Nymph worked on cracking the sophon for an entire day.

By the next morning—

The blue twin-tailed loli sat back in her chair, looking slightly exhausted.

”Master, it’s done.”

”I’ve completely seized control of the sophon and linked its program into your ship’s AI.”

”Well done. Go get some rest.”

Setsuna patted her head and pulled up the main console.

On the holographic screen appeared a line of text:

[Sophon Unit 1 ready, awaiting orders.]

The sophon’s voice was that of a cold, emotionless girl.

”Oh!”

The shipgirls crowded around curiously.

”A robot the size of a fundamental particle? Commander?”

”According to the original story, it could monitor the entire world and block science. What do you plan to do with it?”

”…”

Setsuna thought for a moment.

”In the future, we’ll manufacture more sophons to help manage our vassal worlds.”

”As for this one… I think letting it continue monitoring the Trisolaran schemers would be perfect.”

He issued the command through the holographic interface:

”Monitor all activity on Earth. Report any hostile intent immediately to the Angeloid.”

”Understood.”

The sophon could simultaneously observe all communications on Earth and intelligently analyze their content.

Just as the Trisolarans once had, under its all-encompassing surveillance, privacy no longer existed.

If it wished, it could even tally how many words a random person spoke each day, or how many grains of rice they ate.

This higher-dimensional AI could observe everything except thoughts themselves—perfect for monitoring vassals and colonies.

”Oh, one more thing.”

Setsuna remembered.

”To prevent these humans from causing trouble, lock down their science again.”

...

”???”

When Earth’s people learned they would again be monitored by sophons and their technology locked, their minds collapsed.

Before the aliens came, they had been watched by sophons, their science blocked.

After the aliens came, they were still watched by sophons, their science blocked.

Wasn’t this exactly the same?!

No—worse.

Back then, at least they had been a spacefaring civilization under suppression.

Now, they were directly confined to pre-space times.

Some tried to organize protests, but before their plans could even begin, every detail was reported to Grey and the Angeloid by the sophon.

In the planetary office—

The nanobot scowled at the sophon’s compiled reports and slammed the table.

”Damn it, Commander!”

”Earth here seems way too urbanized. These schemers have nothing better to do than stir up trouble?!”

Considering that most of Earth’s ambitious had left with Starship Earth, what remained were insects.

All day they dreamed up nonsense.

Some even imagined creating a new Wallfacer Plan against the Starsea Empire.

Luo Ji repeatedly reported that people harassed him to launch some so-called ’curse’ against the Eternal Snowfall.

”Handle it however you want.”

Setsuna gave Grey full authority.

”Then I won’t hold back.”

With the Angeloid, the nanobot carried out a sweeping purge on Earth.

At the UN headquarters, they erected a stone stele dozens of meters tall.

Upon it, Grey personally inscribed a poem expressing his governance policy:

Deceivers sharpen blades in the night, Empire’s star sways, Mars glows bright.

Turning heaven and earth anew today, why spare labor when killing’s the way?

Trisolaran schemers—kill! Saints—kill! Singers of false civs—kill!

Alien scum and schemers alike, the Starsea Emperor says: Kill, kill, kill!

”???”

Whenever Earth’s people saw the stele, they were reminded of a figure from history, and shivered involuntarily.

...

Half a month later—

The nanobot reported back to Setsuna.

”Commander, the Earthlings now acknowledge themselves as your loyal subjects. They are willing to serve the Empire like beasts of burden.”

”Even if it means eating husks and swallowing gruel daily, they will never complain.”

”Oh, good results in governance.”

Setsuna praised briefly.

”Just one small issue.”

Grey scratched his head.

”Seems a few countries and about four billion people are… missing.”

”...”

”No problem. That’s fine.”

...

Vmmm—

A small ship carrying Setsuna and several shipgirls cruised outside Earth’s atmosphere.

Grey’s governance of Earth had been astonishingly effective, and everyone wanted to see for themselves how the nanobot had managed to subdue the schemers into obedience in such a short time.

It was also a chance to inspect their new territory.

Setsuna had originally planned to let the humans here live freely, building only a research station on the starbase while leaving both sides to their own devices.

But after Grey’s intervention, Earth’s people now pledged near-fanatical loyalty to the Starsea Empire, willingly submitting as a vassal state.

Every few days, new petitions arrived.

The general message: from now on, Earthlings would gladly serve the Empire as beasts of burden. Even with technology sealed, reduced to pre-space natives, they would not complain.

Their only request: that the nanobot restrain its terrifying powers and spare them.

”How did you manage this? As far as I remember, the mobs here were far more unreasonable than those in other vassal worlds. Much harder to control.”

Bismarck asked curiously.

She had overseen other vassal civilizations. Most pre-space natives were obedient enough—so long as they were fed and clothed, they never entertained strange ideas.

”Organics are foolish. Their feeble brains and limited information-processing can’t rationally analyze benefits and risks.”

”They’re easily swayed by vague ideals, making extremely stupid choices under the incitement of a few.”

”Thus, the quickest and most direct method is simply to physically eliminate them—and let the rest live in fear.”

Grey crossed its arms proudly.

Then it realized it had just insulted all organics with a broad stroke, and hurriedly corrected itself:

”Ah, no, Commander, I meant everyone except you is an idiot.”

”???”

The shipgirls, considering themselves essentially warships rather than organics, didn’t mind.

Gudako, however, was dragged into it and scowled.

”What about me?!”

”I don’t think you’re very smart either.”

The nanobot tilted its head.

”Do you know the Grand Unified Theory? Do you understand entropy recursion? Can you explain a fourth-order singularity??!”

The rapid barrage of questions left Gudako dizzy.

She couldn’t handle arguing with the nanobot.

Its thought processes were utterly alien to ordinary humans.

With near-limitless intelligence and flawless logic, it could memorize anything it saw, even knowledge it couldn’t apply.

Even magic was no exception. Debating it on academic matters was self-humiliation.

Only heavyweights like Lucoa or Mio from the magical side could hold their own against it.

Bickering all the way, the ship entered the atmosphere.

But the sight that greeted them was unsettling.

Setsuna felt the continents looked wrong—different from what he remembered.

Half of the British Isles were gone, chunks of the Americas were broken off, Africa and the Asia subcontinent were split down the middle, north and south, as if cleaved by a blade.

Many island chains were missing entirely.

The shifts in the continental plates had drastically altered Earth’s climate.

Cities once hailed as global centers—New York, Tokyo, Frankfurt—were reduced to barren wastelands. Their skyscrapers and antigravity towers had vanished without a trace.

The aftermath resembled a world war.

People looked up at the ship in terror, then fell to their knees in worship.

”Uh…”

The shipgirls had to confirm several times that this was indeed Earth, and not some other planet.

”What happened here?”

”Did some research institute botch an experiment?”

Bismarck pointed toward the Midwest plains of North America.

There, as though erased, a perfectly circular zone several hundred kilometers in diameter had been carved out of the urban sprawl.

Nothing grew within. It was scorched wasteland.

”Oh, Wyoming.”

Grey thought for a moment.

”They were organizing protests. Opposing imperial rule, demanding the sophon blockade be lifted, shouting about freedom of space exploration.”

”Chanting slogans like ’Give me liberty or give me death’—the usual white-left nonsense humans spout.”

”A few leaders were ready to sacrifice themselves—martyrdom, they called it. Said their deaths would awaken the people… a whole crowd of journalists showed up too.”

”And what did you do?”

Bismarck pressed, more curious now.

Trisolaran schemers had long loved taking to the streets. In a sense, it was a habit inherited from the Common Era. Politicians most feared the media’s inflammatory coverage. But Grey clearly didn’t care.

”I dropped a few antimatter bombs on them. Sent them all up to heaven.”

The nanobot shrugged.

”They said, ’Give me liberty or give me death,’ didn’t they? I’ve never seen such a strange request.”

”Later, more people protested—accusing me of violently suppressing demonstrations, violating civil liberties. So I dropped a few more antimatter bombs.”

”After that, no one had any complaints.”

”…Oh, badass.”

Gudako clapped.

Physically erasing the opposition really was brutally efficient.

”You leveled Jerusalem?! Don’t the religious fanatics have a problem with that?!”

Cruising over the Mediterranean coast, Formidable stared at the devastation below, dumbfounded.

”They did.”

Grey nodded.

”I told them superstition was useless. Praying to the Commander was more effective than praying to God—at least the sophon actually delivered their prayers to me.”

”But those idiots claimed their God would smite me. They knelt day and night, begging angels to come down and destroy me. I transformed into a ship and waited a few days—no angel ever came.”

”So I used orbital cannons to send them all to meet their God.”

As Grey spoke, it pointed toward a city square below.

A towering metallic statue of Setsuna, dozens of meters tall, stood proudly at the center.

Citizens prayed devoutly before it, reciting praises and reverently bowing.

Scenes like this appeared everywhere. All religious sites had been replaced.

Setsuna had become Earth’s sole spiritual idol, gaining hordes of fanatics—eerily reminiscent of the ETO’s devotion.

It felt like another worldline where humanity worshipped a Golden Giant.

”...”

The shipgirls were stunned, at a loss for words.

As the ultimate product of technology, the nanobot inherently despised all religions and superstitions. Even if Satan himself appeared, they suspected Grey would dissect him out of academic curiosity.

”And Africa, Asia split in two—what was that?”

”Someone stirred up trouble. So I hit them with gamma lasers a couple of times.”

Grey said matter-of-factly.

”Cutting continents in half with starship weapons is normal, isn’t it? Civilians dying? Don’t sweat the details…”

”...”

Setsuna nodded.

Gudako gave a thumbs up.

”And you, my friend, are truly the Western King of the stars.”

”Of course.”

Grey crossed its arms proudly.

”Do you know how Earth parents quiet children now? All they need to say is, ’The Gray Tempest is coming!’ and the kid immediately shuts up, too scared to cry.”

”...”

The shipgirls exchanged looks.

”Strangely enough… that is kind of badass.”

—

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