Crossover Shipgirls: Building a Dimensional Empire from Scratch

In the following days, Setsuna gave everyone time to familiarize themselves with the situation.

The Heroic Spirits and Spirits were generally uninterested in this kind of hard sci-fi world—their specialty was magic, and fighting space wars with alien fleets on an astronomical scale was hardly their forte.

A few dragon girls simply said, ”Call us when it’s a magic world,” and dove into the library to research the remaining two neighboring worlds.

The shipgirls and science-side researcher lolis, however, showed immense enthusiasm, devouring The Three-Body Problem over and over again.

They strove not to miss a single detail.

Even if the enemy was just a sub-light native civilization, tactically they still deserved respect.

Weakness and ignorance are not the greatest obstacles to civilization’s survival—arrogance is.

Everyone agreed with this sentiment.

So they carefully sorted through the Trisolaran timeline and conducted in-depth studies on every civilization mentioned.

The Three-Body timeline spans centuries, and counting Cheng Xin’s time after leaving the black domain and spending eons in a pocket universe, it stretches even further.

Human and Trisolaran civilizations were only tiny footnotes—fleeting existences that a passing higher civilization could erase with a casual strike.

The Singers and their Homeworld were more powerful, having mastered dimensional-reduction weaponry, and were preparing to two-dimensionalize themselves to survive the universe-wide dimensional collapse.

Beyond them were the Resetters, aiming to restart the universe entirely, and in pocket worlds, super-civilizations broadcasting ultra-membrane signals to the whole cosmos.

Most of these acted as background forces, with scant available information.

It was, in every sense, a bustling space-age world.

Yet the more the shipgirls read, the more something felt off.

Whether among its humans or across the entire universe, something was just… wrong.

”Commander, I think this Trisolaran world is doomed,” Harbin said, slapping three thick books down on Setsuna’s desk.

She pulled out a bottle of liquor, intending to take a swig, but thought better of it and set it aside.

Beside her, Formidable, Musashi, Bismarck, and others nodded in agreement.

”Oh? What’s on your mind?” Setsuna smiled at the ponytailed, short-qipao-wearing shipgirl whose demeanor carried a certain bold charm.

”Are the Trisolaran humans idiots?!”

”And not just any idiots—the dumbest of the dumb?!”

Harbin, always blunt, voiced the soul-piercing question.

”From the moment they learned of the Trisolarans, they couldn’t unite against the alien threat. Instead, they came up with the ETO, Adventists, and all sorts of traitorous nonsense.

”After the Great Depression and the Second Renaissance, they finally made some space-tech progress—only to get so arrogant they sent their entire fleet to be destroyed? If Zhang Beihai hadn’t run for it, humanity would have lost its seed entirely?!

”When Luo Ji was useful, they praised him to the heavens. Once he deterred the Trisolarans, they feared him to death. They didn’t even thank him?‖!

”And in the end, they chose a saint to lead them all to doom???”

...

Harbin’s anger only grew, drumming her fingers hard on the table.

”Commander, those humans are beyond saving.”

Bismarck picked up the thread.

”They have neither the courage to fight the enemy to the end, nor the discipline, and they’re arrogant and foolish.”

”The Trisolarans are no better.”

Setsuna had to admit, among the dozen or so worlds he had conquered or was about to conquer, the Trisolaran world’s humans were certainly the most pathetic.

They combined anti-intellectualism, mob mentality, and naive idealism into one package.

When faced with apocalypse, they threw parties and perfected the art of infighting.

The number of clear-headed individuals on Earth could be counted on two hands.

It was hard to imagine that, under alien threat, Earth’s government could be so utterly incompetent.

In the Stellaris worlds, Earth’s United Nations or the Human Federation completely outclassed these Trisolarans by miles.

”I think… there’s no need to make that Earth a vassal,” Richelieu said after some thought.

”It feels like they’d cause trouble every few days—they’d be hard to manage…”

”We might end up putting in more effort than the returns are worth.”

”Mm…” Setsuna pondered for a moment, then nodded in agreement.

”There’s no need to stay in the Trisolaran world for long. Just take Photoid, Dual-Vector Foil, and other valuable tech and leave.

”At most, we can set up a research station there for high-risk technology and experiments. Since their universe is doomed anyway, we won’t feel bad if it blows up.”

The Trisolaran universe had been battered and broken long ago.

In ancient times, it had been an eleven-dimensional universe.

Time had more than one dimension, and the speed of light was nearly infinite—one could cross from one end of the universe to the other in a single Planck time.

Later, through large-scale wars between civilizations using law-based weapons—dimensional reduction strikes—the universe was gradually beaten down to three dimensions.

Sooner or later, it would likely be reduced to two.

Collapsed 2D spaces and slow-light black domains littered the cosmos, impossible to repair.

Simply put—the pollution was too severe.

Setsuna had no interest in saving an entire universe.

”If it can be reformed, fine. If not, drag it off to power generation.”

...

A few days later—

After the shipgirls had fully familiarized themselves with the Trisolaran situation and finished tuning their gear—

In Earth’s orbit, aboard the Eternal Snowfall—

Hundreds of shipgirls in the expeditionary force gathered on the bridge, gazing out the windows at the starlit void, faces full of anticipation.

As the Empire’s flagship, the Eternal Snowfall would shelter all its companions on campaign.

Setsuna stood at the main console and opened the extra-dimensional star map.

[Trisolaran World (Space Age)]

This universe contains numerous spacefaring civilizations of varying levels of development.

Some civilizations can manufacture law-based weapons to strike enemies, causing severe damage to cosmic space.

No civilization has yet achieved faster-than-light travel.

Comparison of Strengths:

• Technological Level: Like an Ant.

• Military Strength: Like an Ant.

• Economic Power: Like a God.

”…”

Economic strength was now calculated by productivity.

Given that his ten or so vassal worlds couldn’t outproduce the myriad spacefaring civilizations in the Trisolaran universe, that was normal.

As for tech and military levels, the reasoning was obvious.

Sub-light natives had no comparison to an FTL civilization—among technological civilizations, this was pure top-tier crushing.

”Some civilizations can manufacture law-based weapons…” Setsuna read the intro and almost laughed.

”Is this the first world capable of killing itself off? If I arrive too late, will the Trisolaran world have turned 2D or 1D?”

Steadying his mind, he extended his hand, channeling his authority to open a space-time portal.

Shwoom—

A kaleidoscopic tunnel opened in the starry sky above.

Vmmm…

The Eternal Snowfall passed through the long corridor.

After a swirl of temporal-spatial turbulence, the tunnel’s end revealed a dim, cold cosmos.

”Tch, so when you cross over in space, you get dumped into space, huh?”

Setsuna engaged the starship’s thrusters.

With a ship, the exact drop location didn’t matter—near or far, it was all within reach.

Boom!

The Juggernaut descended into the void, the surrounding space trembling.

[Engines: Normal]

[Weapons: Ready]

[Full Ship Diagnostic: Normal]

The AI’s mechanical voice confirmed.

Through the viewport, he spotted a deep-blue planet slowly spinning in the void.

It was far larger than Earth, with planet-wide ice storms raging in its atmosphere.

Around the ship drifted sparse nebulae and small celestial bodies.

”Neptune?”

Setsuna quickly realized they had arrived in the outer Solar System, within the Oort Cloud.

Far away, the Sun was a faint pinprick of light, barely visible.

”Initiate full-scan of this system and a 100-light-year radius.”

Setsuna activated the sensors to assess the surroundings.

Suddenly—

”Commander Onii-chan, over there!”

Unicorn pointed toward the distant void.

In the black of space, two thousand suns appeared.

They were arrayed in a perfect rectangle, emerging in the darkness.

On closer inspection, the ”suns” were the blazing fusion drives at the tails of starships.

Two thousand one hundred and fifty vessels, accelerating slowly from Jupiter’s orbit toward Neptune.

Their formation was immaculate, as if flaunting humanity’s dignity and invincibility to the cosmos.

”Oh? Is that the local human fleet?”

Grey and the shipgirls craned their necks in curiosity.

Meanwhile, the holoscan revealed a blinking dot moving in the opposite direction, farther from the 2,000-ship fleet.

It was another starship, apparently at full thrust, trying to escape the Solar System.

A few ships behind it were starting up, preparing to give chase.

Intercepted comms carried voices from the fleeing vessel.

A deep male voice spoke with a younger woman.

”You are a qualified captain, Dongfang.”

”Where are we going?” the young woman asked.

”…Wherever it is, it’s a more responsible choice than staying here.”

His voice carried a quiet thrill as he recited the command he had pursued all his life:

”Natural Selection—Proceed to Four.”

”…”

...

”What is this? Are they planning to welcome me with two thousand salvos?”

Setsuna trailed off.

The Doomsday Battle.

He and the shipgirls instantly understood the situation.

At this moment, the Trisolaran probe had just arrived in the Solar System, and humanity’s fleet had mobilized in full to face the Droplet.

Zhang Beihai had fulfilled his lifelong wish and was piloting the Natural Selection in escape.

Cheng Xin’s ally, Tu Hengyu, had long been ready—evacuating the ship’s atmosphere, topping up fuel, and now giving full chase from behind.

At this time, human confidence had swelled to unprecedented levels.

Under the technological blockade of the sophons, humanity had nevertheless built starships using controlled nuclear fusion, achieving speeds of 15% of light speed—faster than the Trisolaran First Fleet’s 10%.

This speed advantage gave humanity the courage to face the Trisolaran fleet in battle, even though their foundational sciences were frozen.

Of course, the outcome would be nothing more than setting off a 2,000-round fireworks show in the Solar System.

”Hmm…”

”Aren’t their ships a bit too backward? Can these even get into space?”

Grey tilted her head, using the Eternal Snowfall’s sensors to scan the ships.

The human United Fleet’s vessels were all standardized in design, looking quite similar.

Each was about the size of three aircraft carriers—smaller than the Starsea Empire’s interstellar frigates—and driven by controlled fusion engines.

They carried gamma-ray lasers, electromagnetic kinetic cannons, infrasound hydrogen bombs—common weapons for natives first venturing into space.

From Setsuna and the shipgirls’ perspective, their speeds were akin to crawling through the void.

The sensors then picked up a small craft beyond the Solar System, heading toward the fleet.

It was tiny—just over three meters, smaller than a carrier-based fighter.

Its shape was that of a droplet: a rounded head, sharp tail, and a flawless mirror-like surface reflecting the Milky Way as smooth light patterns.

The Droplet’s speed was far greater than that of the United Fleet, and they were expected to meet soon within the Solar System.

On the star map, the United Fleet, the Droplet, and the newly-arrived Eternal Snowfall formed a triangle.

Thanks to advanced optical camouflage and electromagnetic jamming, neither the United Fleet nor the Droplet had detected the massive Juggernaut appearing on the far side of the Solar System.

”Commander, they’re about to crash into each other. So… what should we do?”

Grey pulled out a pile of sunflower seeds and drinks from her pocket, stacking them on the console and calling the shipgirls over.

”How about we watch the 2,000-round fireworks first—call it a salute to the Emperor’s arrival?”

”I’m in!” Ritsuka Fujimaru raised a hand.

”Hah?!”

The shipgirls realized these two’s moral compass was… chaotic. Humanity’s folly went without saying, and nanomachines didn’t exactly measure good and evil in normal ways.

Grey, in fact, looked down equally on everyone except the Commander.

Bonk—Bonk—

”Ow!”

Setsuna flicked both of them on the forehead.

”Go. First, capture the Droplet for me—the science lolis have been begging for one to study.”

Boom—

From the Eternal Snowfall’s stern erupted a plume of ghostly blue light as it surged forward.

...

On Earth—

Humanity was in a state of unprecedented confidence and fervor.

The Second Renaissance and advances in controlled nuclear fusion had allowed them, in a short time, to build a massive space navy fleet, large enough to blot out the sun.

They held full confidence in the Doomsday Battle. Though it would decide Earth’s fate, almost no one outside the ideologically sealed-off camps believed humanity could lose.

The United Nations had even begun planning how to deal with the defeated Trisolarans.

This included debates on whether the Trisolaran fleet should be given living space within the Solar System, whether Trisolaran immigrants should be accepted, and if they should be integrated into human society.

This plan was called the ”Sunshine Project.”

Earth’s people decided to show the Trisolarans their strength, magnanimity, and humanitarian concern.

Not long after, a piece of news sent humanity into a frenzy:

”The International Fleet has reached a decision.”

”All stellar-class battleships of the Asian Fleet, European Fleet, and North American Fleet—2,015 ships in total—will form a United Fleet to intercept the Trisolaran probe that has already crossed Neptune’s orbit!”

Through a live broadcast relayed from Jupiter’s space military base, people watched as two thousand stellar-class warships, blazing with brilliant light, slowly advanced toward the outer Solar System.

Under the light of two thousand suns, Jupiter and its moons seemed to burn.

And their interception target was nothing more than a single Trisolaran probe.

The Earth erupted into celebration. Some wept tears of joy, others cried out in excitement, and many joked with the confidence of the strong.

”All this for one tiny probe?”

”This is like using two thousand butcher’s knives to kill a chicken!”

”Exactly, two thousand cannons to hit a mosquito! What is this?”

”Come on, understand the International Fleet—this might be their one and only battle against the Trisolaran world.”

”Yeah, if you can even call it a battle.”

”Well, fine—just think of it as a parade of human civilization’s might. A super fleet like this? It’ll scare them to death—if they even have bladders to empty!”

”Hahahaha…”

The United Fleet advanced in a dense parade formation, each ship just twenty kilometers apart—practically side-by-side in space.

This was to ensure every ship could be counted as participating in the interception. No one wanted to be excluded from the honor.

Two thousand warships, like two thousand little suns, pushed forward.

On radar, the Droplet was now visible.

50,000 km…

35,000 km…

10,000 km…

Finally, the United Fleet maintained a distance of 1,000 km from the Droplet.

This was calculated to be safe—even if the Droplet self-destructed via matter-antimatter annihilation, the blast would not reach them at that range.

Through this proximity, both the fleet and Earth’s viewers could now see the Droplet’s precise form.

It looked so delicate—simple yet beautiful.

The liquid-like surface was so lifelike that observers sometimes thought it truly was a liquid, not a machine.

”It’s beautiful—like the Virgin’s tear,” a female officer aboard one ship said.

Her comment struck a chord. People began to suspect it might be a gift from the Trisolarans.

At the edge of the United Fleet, inside the stellar-class battleship Quantum, an elderly man with white hair was packing his equipment: electron microscope, geology hammer, thermal sensors…

Ding Yi, Earth’s most renowned scientist, was to be the first to approach the Droplet in a small shuttle to study it up close.

The risk was enormous, but his thirst for knowledge had long since eclipsed fear.

”I have a bad feeling,” Ding Yi said, tapping his pipe against the Droplet’s holographic image.

”Why? It looks like a harmless work of art,” a military officer replied.

”That’s why I feel bad,” Ding Yi frowned. ”If something strays too far from our expectations, it’s never a good sign.”

He sensed unease. Humanity’s recent achievements were astonishing—victory over the Trisolarans seemed inevitable. But as a scientist, he knew their fundamental science hadn’t advanced in centuries.

”Children, do you know what I’ve been doing all these years? Teaching physics at university. Even supervising PhD students. Me—a man from two centuries ago—still teaching physics. Ha…”

He shook his head and looked outside.

Suddenly, in the dark void, he spotted something out of place: a bright point of light moving from Neptune’s orbit toward the United Fleet and the Droplet.

At first, Ding Yi thought it was one of the United Fleet’s ships, but quickly dismissed the idea.

It was far too large—so big it could be seen with the naked eye from this distance. And it was moving fast, like a meteor streaking across the Solar System.

As a key figure in starship and fusion research, Ding Yi knew human ships couldn’t reach such terrifying speeds.

”Something’s approaching from Neptune’s orbit,” he reported.

After rapid escalation, the Quantum’s captain and the entire United Fleet went on alert.

The ships’ radars swept at maximum power, detecting nothing.

”Nothing, Professor Ding. Aside from us and the Droplet, the Solar System’s empty,” the comms officer said.

”Outside! Use your eyes! Stop trusting those stupid instruments!”

Ding Yi slammed the porthole, shouting.

One by one, crew members turned to look—then froze.

A starship, thousands of times larger than a stellar-class battleship, the size of a small moon, was gliding through the cosmos.

Its vast hull, on an astronomical scale, was nearly as long as the United Fleet’s entire two-thousand-ship formation.

Its main axis stretched for thousands of kilometers, with vast weapon wings blotting out the stars—each turret and gun far larger than a human stellar-class warship.

Ding Yi didn’t know what a Tachyon Lance or Focused Arc was, but he knew these weapons dwarfed anything the United Fleet had.

A moon-sized warship—this defied all human physics and engineering.

A simple truth hit him: a stellar-class battleship, the size of three aircraft carriers, could wipe the surface of Earth clean and destroy nations with ease.

So what could a ship the size of an asteroid do?

Who was it? Where had it come from? What was it here for?

A storm of questions filled his mind.

In the end, he could only blurt out one thing:

”Foolish children—run!!!”

—

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