Crossover Shipgirls: Building a Dimensional Empire from Scratch

Clang—

The Eternal Snowfall, carrying the wreckage of the Singer’s ship, descended near the Solar System’s starbase.

This starbase was much smaller than the one in the capital, consisting mainly of research facilities and defense modules. It had no shipyards or starship assembly plants.

In the Trisolaran universe, building a starbase had only one purpose: to research this universe’s technologies.

To the Starsea Empire, every civilization in the Trisolaran cosmos was nothing but a sub-light native.

Even the so-called strongest god-level civilizations had only barely brushed against lightspeed, completely powerless before the FTL overlords of the Stellar Era.

But in terms of technological depth, they had gone impressively far—with sophons, photoids, dual-vector foils, and even later, artificial pocket universes.

Each more spectacular than the last.

”Oh, Commander, finally something interesting.”

”The shipgirls keep bringing back nothing but natives and their ships. Other than putting them on display in museums, those antiques have no research value.”

Kayo Senju, leading her loli research team, eagerly urged the Angeloid to move the wreckage into the lab.

Even before departure, they had been fascinated by the Singer’s civilization.

After all, dimensional technology was still virtually a blank field for the Starsea Empire.

”Hm?”

Setsuna noticed that the starbase docks were piled high with ships of all shapes and sizes.

All were trophies of the shipgirl expeditionary fleets.

Around the Solar System, they had fought far and wide, crushing natives with their FTL advantage, then bundling up the aliens and their ships as spoils of war to bring back.

”What level are these ships?”

Richelieu asked curiously.

”The fastest ones use curvature drives, reaching barely lightspeed. Most are between five and twenty percent lightspeed, powered by antimatter or fusion engines.”

One of the loli researchers explained.

As she spoke, she pointed at a ship roughly the size of a battleship.

Dozens of Angeloids were unloading what looked like cryogenic pods from it.

”Oh, there was also one particularly imaginative civilization. Their ships couldn’t even reach one percent of lightspeed, yet they still tried interstellar colonization.”

”Their method was to stick crew into stasis pods for hundreds of thousands of years, relying on the ship’s AI to navigate to the target star system and then awaken the colonists.”

”When Veneto, Zara, and Pola found them, the entire crew was frozen stiff.”

”...”

The shipgirls listened in amazement. Truly, the vast cosmos held endless oddities.

Some civilizations, thanks to wildly skewed tech trees, ended up on bizarre developmental paths.

A blue-haired, dragon-horned Eastern shipgirl lugging a giant ladle walked up to the cryogenic pods for a closer look.

She knocked on the glass.

”Hmm… are these fungi? I wonder if they’re poisonous~?”

”Can I borrow one to experiment? I wanna add some scallions, ginger, and garlic and see how it tastes if I boil it…”

”???”

Veneto, in charge of the operation, was horrified.

”You Eastern shipgirls really try to cook everything?! These are aliens, for heaven’s sake!”

”Lung Wu, step back.”

Yat Sen called the little shipgirl back, tapping her on the head.

”The Commander said aliens are for zoos, to be put on display. Understand?”

”Uu…”

Lung Wu held her head, looking pitifully at Setsuna.

”But they really look just like the mushrooms I cooked before.”

”...”

Setsuna’s face darkened.

”Great, I’ve completely spoiled the shipgirls. Now they’re all learning how to make alien stew.”

...

Kayo Senju’s team spent several days studying the spoils from the Singer’s ship.

The loli researchers worked day and night, dismantling everything—the hull materials, structure, computers, and all the weapons aboard.

Everyone was deeply curious about this mysterious civilization that had destroyed the Solar System in the original storyline.

Setsuna even gave Kayo a few dual-vector foils, sternly warning her to be careful. He also brought in Grey and the Siren shipgirls to keep watch.

A few days later—

The little loli reported her findings to Setsuna.

”Commander, we’ve completely dismantled the captured Singer ship.”

”Other than the crew, who were all killed by high-energy radiation weapons, the rest of the ship’s components were intact.”

On the holographic display, Kayo Senju laid out a variety of research projects.

Her sharp and professional demeanor made her look nothing like a girl barely over ten years old.

”The ship’s engine is a curvature drive, the most common type of lightspeed engine in the Trisolaran world. Its hull materials and conventional weapons are unremarkable—more advanced than the Trisolarans, but far inferior to us.”

In just a few sentences, she assessed the Singer ship’s overall tech level.

”However, we did find something interesting in its onboard AI.”

”The Singer’s vessel is called a ’seed ship.’ They depart from the homeworld with the purpose of cleansing other civilizations in this universe.”

”The reason, well… Ye Wenjie mentioned it a long time ago.”

Setsuna was already familiar with the two axioms of cosmic sociology.

First, survival is the foremost need of civilization.

Second, civilization continuously grows and expands, while the total amount of matter in the universe remains constant.

The more civilizations there are, the fewer resources each receives.

The shipgirls had found many hidden civilizations within 200 light-years of the Solar System, which meant the Trisolaran universe was actually crowded.

Thus, for a civilization to gain more resources and eliminate threats before they could rise through technological explosion, exterminating lesser civilizations became inevitable for higher civilizations.

”Dark. This universe is just too dark.”

Gudako found the background of the Trisolaran universe incredibly brutal.

”Where’s the Singer’s homeworld?”

Setsuna asked.

”Hmm… judging from its route, we estimate it’s in the Large Magellanic Cloud, or even farther.”

”The seed ship has been traveling for seventy thousand years—measured in its own reference frame. Considering relativistic effects, the actual distance would be even greater.”

Kayo Senju projected the ship’s flight path. Its starting point was in a star cluster 160,000 light-years away.

Even for FTL starships, that was quite a distance.

”Tch, I was hoping it’d be close so we could just wipe out the homeworld. Guess we’ll shelve that for later.”

Setsuna jotted down a note in his little notebook.

Most of the Singer civilization’s valuable assets were already on the ship, so destroying their homeworld wasn’t urgent.

Besides, the homeworld and the fringe worlds were locked in a heated war, both preparing to descend into two dimensions together.

By the time he got there, the place might already be nothing but empty two-dimensional space.

”Anyway, the other things of value are the photoids and dual-vector foils you brought back, Commander.”

Kayo Senju had the Angeloid bring up a small metallic sphere.

Its material was unknown, its surface gleaming faintly.

”Photoids, also called mass-points. Most advanced civilizations use them for Dark Forest strikes. The Singer ship carried several hundred of them.”

”When launched, they accelerate to near lightspeed in a short time, their relativistic mass skyrocketing. They’re usually aimed directly at a star.”

”With sheer kinetic energy, they disrupt a star’s structure, triggering its explosion and annihilating the entire system.”

Grey had once remarked that for a technological civilization, destroying a star wasn’t difficult—just a matter of knowing the trick.

Photoids were the simplest, cheapest, most casual anti-stellar weapon.

Toss one, and you could blow up a sun.

”…Can we build them?”

Richelieu asked intently.

”Of course. They’re not technically complex at all—they just exploit physical laws. A very clever weapon.”

”We can retrofit our gigaton-class kinetic cannons into photoid launchers. Much cheaper than missiles.”

The little loli tapped on the holographic screen.

”Hiss… photoid launchers? Could we all be outfitted with them?”

”Battleships, carriers, cruisers, even destroyers?”

The shipgirls realized their firepower was about to expand dramatically.

”Mhm. If the Singer’s seed ships could carry them, then everyone can.”

”In the future, you’ll all be armed with Anti-Star Noble Phantasms.”

Grey nodded in agreement.

”Otherwise, it’s too much trouble for the Commander to be the only one crushing stars. Against other interstellar empires, we can all put on fireworks shows.”

”...”

A magnificent vision filled everyone’s minds.

The shipgirls of the Starsea Empire, blotting out the skies, sweeping across enemy star systems at FTL speed.

Photoids streaking like meteors across the void, stars shattered by the cluster, entire civilizations spanning galaxies obliterated in an instant.

Breaking stars, extinguishing suns, all in the blink of an eye.

...

Starship shipgirls already had medium- and close-range kinetic weapons installed on their hulls.

Adapting them to fire photoids wasn’t complicated—the principles were the same. The only challenge lay in producing photoids, which required some special materials.

Given the Empire’s abundant resources, it wouldn’t take long before all starship shipgirls could be outfitted with photoid launchers.

Some battle-hungry shipgirls were already thrilled, eager to start ”more efficient” enemy cleansing.

Then—

Everyone’s attention shifted to the most brutal weapon from the original Three-Body novel.

Kayo Senju led the group through winding corridors of the research sector.

They arrived at an isolated experimental zone, separate from the starbase, guarded heavily.

It floated in space like a lone island, accessible only by shuttlecraft. Around it hovered defensive turrets and squads of Angeloids on watch.

Everyone underwent multiple identity verifications—even Setsuna himself.

Such strict security was rare even at the capital’s research institutes.

The building itself was a hemispherical dome. The moment they stepped inside, the shipgirls felt something strange.

Each of them experienced an uncomfortable sense of pressure.

”This is the dimensional technology testing zone. The entire sector is independent from the starbase and shrouded in forcefields.”

”If an accident occurs, the whole facility can be destroyed instantly and sealed by protective fields to prevent dimensional collapse from leaking.”

Kayo Senju explained.

”Hiss—”

Several little shipgirls gasped.

Researching law-based weapons naturally demanded proper caution.

Otherwise, Setsuna wouldn’t have moved the experiments into the Trisolaran universe. If something went wrong back home, it would be unfixable.

If disaster happened here, at worst they could just abandon it and run.

Entering the experimental hall, they saw not only loli physicists, but also several Sirens, along with Akashi and Daedalus.

The finest minds of the Starsea Empire had gathered, surrounding a spherical glass chamber, observing a floating white slip of paper inside.

On holographic displays, they scribbled equations and pored over torrents of data.

”Yo, Commander, you really brought back something wild this time?!”

Purifier waved cheerfully.

”Dimensional reduction… tsk tsk, we could scare the Arbiter fleet to death with this! Their databases don’t have anything like it.”

”Maybe it’s time to promote us and demote the Arbiters…”

”Are you trying to overturn the heavens?!”

Observer smacked the excitable one with her tentacle rigging.

”Strength decides who rules as Arbiter!!”

The two Sirens bickered noisily, while Compiler silently studied the data. Occasionally she glanced at her colleagues with the expression of someone watching idiots.

”We’ve conducted small-scale experiments on dividing the dual-vector foil, Commander. In some ways, it’s an even simpler, cruder weapon than the photoid.”

Kayo Senju and Grey explained.

”In essence, it’s just a two-dimensional space sealed in a forcefield. To use it, you simply toss it into the enemy’s world.”

”Once the field dissipates, three-dimensional space collapses into two, dragging the entire universe down with it.”

”Using a dual-vector foil requires no technical skill or threshold. Even primitive natives could drop it from a plane like a bomb—”

”—As long as they don’t mind mutual destruction.”

Weapons of the Trisolaran universe gave Setsuna the sense of ”great truths in simple forms.”

No flashy or convoluted technology—just the most direct applications of cosmic law.

”Could they be mass-produced?”

Bismarck asked.

”You could have as many as you want.”

Grey shrugged.

She operated the console.

The forcefield containing the dual-vector foil gradually dimmed, releasing the two-dimensional space.

”The foil’s leaking!!!”

Several little shipgirls panicked, ready to bolt.

The glass dome hummed as invisible energy beams fired from the slots, splitting space apart.

In the blink of an eye, the single pale-white slip had become two.

Graceful and weightless.

One dual-vector foil had become two.

”We released the forcefield restraining the two-dimensional space. In the instant it began expanding, we cut it and re-sealed it—creating more dual-vector foils.”

”Of course, this process must be completed within one nanosecond. If the two-dimensional space expands too far, no one can stop it.”

Grey explained it lightly, but everyone else was shaken.

”Doesn’t that mean manufacturing dual-vector foils is virtually costless for us? We could mass-produce them?!”

Richelieu blinked.

”That’s right. As long as our precision is high enough, it only costs a bit of electricity. If needed, we could produce several hundred a month.”

”No wonder everyone in the Trisolaran world uses them—even the Singer, just a janitor, relied on them. Cheaper than corrosion missiles.”

”Hundreds?!”

The shipgirls were stunned.

”Mhm. If the Commander wished, we could deploy enough dual-vector foils in a short time to dimensionally strike an entire galaxy cluster.”

”Of course, not in our universe.”

Grey folded her arms.

For FTL starships, using dual-vector foils was entirely different from lightspeed natives.

By jumping across regions of the galaxy, a fleet could scatter countless foils.

As they expanded, they’d connect from points into sheets, forming a vast two-dimensional space that swallowed the entire Milky Way.

”Is there a more controlled, efficient improvement possible?”

Setsuna pondered.

The weapon was powerful, but inefficient. The foil’s maximum spread was limited to lightspeed, unable to catch FTL ships.

Worse, using too many risked suicide.

”Extremely difficult. It will take time to research and experiment.”

Daedalus and Compiler answered together.

”Three-dimensional space collapsing into two never stops, so dual-vector foils are inherently uncontrollable.”

”But the concept of dimensional strikes is advanced. We’d like to find alternate methods—like restricting collapse to a star system, or just a few light-years.”

”In the ideal case, a starship could, like the Fallen Star Lance, deliver an instant, directional dimensional strike on astronomical scales.”

”We’ve drafted 128 preliminary experimental proposals…”

”Additionally, we could reference Synapse…”

Daedalus slipped into scientist mode, lecturing endlessly on advanced theory.

Not only the shipgirls—even Akashi looked utterly lost, her eyes swirling. She realized she couldn’t keep up with these scientific maniacs.

So she flopped into Setsuna’s arms, twitching her ears, playing cute to beg off.

”Commander, I really don’t understand this dimensional tech. Can I just go back to the capital and fix shipgirl gear, nya?”

”Sure. Warm my bed and you’re forgiven.”

Setsuna ruffled the cat-eared girl’s head.

”Meow meow??!”

”Ahem—”

After speaking for more than ten minutes, Daedalus cleared her throat.

”Commander, do you understand?”

”Yeah. You want to make a controllable version of dimensional weapons. Whatever you need, ask.”

Setsuna skipped the details, extracting the core meaning.

”In this universe, experiment however you like—just not too close to Earth. If you need experimental sites in other systems, I’ll open the way.”

He knew many star systems would be sacrificed to dimensional weapon research.

But here, in the Trisolaran world, it didn’t matter. Plenty of civilizations already used two-dimensional strikes—one more wouldn’t hurt.

”Mm…”

”Also, the manufacturing process for dimensional tech is a challenge. It requires extremely advanced physics and string theory knowledge…”

Daedalus hesitated.

”That’s simple. Manufacturing is never a problem for the Starsea Empire.”

Setsuna gestured. Yat Sen brought in a few colorful Bulins from outside.

Leading them was the foreman Bulin, the one who had built the Eternal Snowfall, staring at Setsuna with wide, innocent eyes.

”Commander, do you want us to build another ship, bruin?!”

Foreman Bulin beamed with confidence.

”No. This time, I’m giving you a new task.”

Setsuna patted her head, pointing at Daedalus and Compiler.

”Go with them. You’ll be building dimensional strike weapons.”

”Buli?!”

Bulin tilted her head, thinking hard about what Setsuna meant.

Then she slammed the floor with her hammer in protest.

”Commander, are you picking on Bulin, buli??!”

—

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