Crossover Shipgirls: Building a Dimensional Empire from Scratch

Solar System Starbase.

The towering hull of the Eternal Snowfall floated outside the base.

In the Juggernaut’s spacious lower docks, dozens of shipgirl starships were moored side by side.

Specialized Bulins held Ultra Rainbow Hammers in their hands, tinkering with the armed modules on the shipgirls’ hulls.

They dismantled the original colossal gigaton-class kinetic cannons and, by hammering in ways that defied physics, transformed them into another weapon of even larger caliber.

Bang bang bang—

A group of Bulins hammered around a turret, then measured its caliber with a photoid.

”Too small.”

Bang bang bang—

The Bulins hammered again, then measured once more.

The photoid could now just barely fit inside the launcher. Satisfied, they nodded.

They then fixed the modified photoid launcher onto the shipgirl’s hull.

”Belfast, your main gun has been refitted, bruin!”

”Next, next one is Sirius…”

A Universal Bulin hopped onto the nearby silver-white starship, continuing to use her universal Bulin tinkering powers to modify the shipgirl’s equipment.

Not far from the docks, inside the assembly factory—

The Angeloids were delivering cargo ship after ship of materials into the automated production lines.

The required components were quickly processed and produced for the Bulins.

As a mobile space fortress, the Juggernaut carried several integrated starship production and repair lines.

Even without a dock, shipgirls under its command could be swiftly repaired and modified.

Combined with the many Bulins and Angeloids carried aboard—

Wherever they went, ships could be built.

If resources were insufficient, they could simply mine on-site.

With so many civilizations in the Trisolaran universe destroyed, just from shattered stars and planets alone, countless high-quality minerals could be harvested.

...

The weapon modifications for the shipgirls proceeded at astonishing speed.

Since the principle behind photoids was extremely simple—essentially just accelerating a mass-point to near-light speed, using relativity to destroy a star—

It involved no complicated physics or engineering. As long as the materials were adequate, it was enough.

Thus, in less than half a month—

Most shipgirls, including the Eternal Snowfall herself, had been equipped with new photoid launchers.

Boom—

The fleet activated their warp engines, leaping through the void.

They arrived at a star system thousands of light-years from the Solar System.

Inside their hulls, the shipgirls curiously observed their new weapons.

Each hull now carried several massive turrets.

Their design resembled the railguns of the Common Era, but on a far greater scale.

Just the barrels were nearly 500 meters long, with enormous bases beneath.

[Photoid Launcher]

A terrifying weapon capable of destroying stars.

Destroyer-class shipgirls generally mounted two or three. Cruisers carried more. Carriers and battleships, over a dozen was common.

On the Eternal Snowfall’s weapon wings, the number of these gigantic turrets exceeded one hundred.

”Wait, I thought it was one per person?”

Formidable blinked.

She felt it was strange for a single starship to mount over a dozen anti-stellar weapons.

”Um, according to Grey’s design, we made some optimizations to the photoid launchers, buli.”

”They’re not only for destroying stars—at medium and close range, they’re also extremely efficient kinetic weapons, perfect for striking enemy ships in sub-light states.”

A Bulin scratched her head, explaining to the shipgirls.

”And since their principles are simple and costs low, the Commander said everyone can install more.”

”...”

”Install more of these?!”

”Commander, has your firepower deficiency syndrome reached its final stage?!”

Formidable stared dumbfounded at the Eternal Snowfall’s weapon wings, lined with rows upon rows of photoid launchers.

”This is called efficiency.”

Setsuna answered calmly.

Several little shipgirls couldn’t wait any longer, immediately starting to play with their new toys.

”Ohhh, I can smash stars like the Commander now!!!”

Buzz—

Several destroyer-class shipgirls sailed out from the Eternal Snowfall’s docks.

”Don’t you dare target the Solar System! And don’t touch the stars near it either!”

Yat Sen’s stern voice came through the comms.

”In the Trisolaran universe, you can play however you want. But when we return, you are not allowed to randomly attack our stars.”

Setsuna chuckled and added a reminder.

Stars in his own universe and vassal worlds would eventually be used for resource development. Using them as target practice for star-destroying weapons would only be wasteful.

The Trisolaran world, however, was positioned as an experimental ground, free to use as they pleased.

After all, this universe would eventually be two-dimensionalized anyway, so better to squeeze out its remaining value.

”Got it, nanoda!~”

Yukikaze replied cheerfully.

She led a few small destroyer shipgirls to a star not far away.

Bang—Bang—Bang—

They locked onto the target and fired in quick succession.

The photoids shot out, dragging behind comet-like blazing tails, flying at near-light speed straight into the star’s outer shell.

Boom—

Minutes later—

The star’s chromosphere and photosphere were pierced through. Its outer layers collapsed under gravity, spewing stellar material outward.

Nearby planets on close orbits were scorched into molten lava worlds.

Then, as its internal stability was destroyed, the star underwent a violent chain fusion reaction, triggering an unprecedented explosion.

BOOM!!!

Several planets were engulfed by the expanding star, bloated thousands of times larger, while others were shattered into fragments by the cosmic shockwave.

Only those on the far orbits barely escaped unscathed.

”Whoa…”

The little shipgirls stood dazed for a moment.

It was their first time wielding such destructive power.

Photoids didn’t have the ultra-long-range, instant-strike capability of the Tachyon Lances, and in interstellar battlefields measured in light-years, FTL energy weapons still reigned supreme.

But in medium- and close-range battles, the effect was overwhelming.

After winning a space war, if they didn’t feel like occupying the enemy’s system, they could just quickly wipe out the enemy’s homeworld.

No orbital bombardment required.

If photoids could shatter suns, they could certainly smash planets into pieces as well.

”So strong… does this mean we now count as having star-level power?”

Tai Yuan asked, peeking curiously.

She felt a strong sense of unreality. In her old impression, destroying a star was something only top-level beings could achieve.

But in the Trisolaran world, it felt absurdly easy—just toss a photoid.

”That’s what happens when the tech tree is skewed.”

Setsuna laughed.

”Hey hey hey, I’ve got a good idea.”

Fu Shun perked up, gathering the Four Kongous, along with Lung Wu, Hu Pen, and a few other small shipgirls. She pointed toward the distant starscape.

”…How about we see who can hit more accurately?”

”Good idea!”

The little shipgirls thought this sounded like a fun game.

A few years ago, they had played marbles in the port area. A few years later, they were in deep space playing target practice with photoids on stars.

Their tastes had certainly gone up a level.

Each picked out a few stars.

Bang—Bang—Bang!!!

Dozens of photoids streaked across the cosmos in succession.

If any uninformed Trisolaran natives were to see this, they’d definitely cry out: ”Holy crap, which advanced civilization is committing genocide?!”

”Commander, Commander! Help me calculate—do you think I can hit a star 30 light-years away?”

Fu Shun realized she couldn’t properly calculate an ultra-long-distance trajectory on her first try with photoids, so she turned to Setsuna for help.

”….”

Setsuna activated the Eternal Snowfall’s sensors and shipborne AI.

A quick scan showed the photoid’s speed was sub-light, its trajectory nearly a straight line, and it would precisely strike a distant, unfamiliar star system… thirty years later.

”No problem. But if you want to see the result, you’ll have to wait three decades.”

He answered casually.

Then, suddenly, the sensors gave an anomaly alert.

In the star system set to be destroyed thirty years later, there existed an unknown alien civilization.

They had just stepped into the space age, with technology similar to early human levels.

They were celebrating in orbit, cheering for their first successful spaceflight.

The alien civilization had no idea—and could never have realized—that in thirty years, a photoid would pierce their home system.

”Well, good luck to you then.”

Setsuna yawned, with no intention of intercepting it.

”Little shipgirls don’t understand, just tossing things for fun.”

...

The Eternal Snowfall cruised slowly through the void.

Setsuna did not join the little shipgirls in their revelry.

After clearing out the Solar System’s surroundings, smashing stars had already become boring.

He checked the hull. On each of the two weapon wings, 64 photoid launchers had been installed.

The Juggernaut’s enormous size allowed him to mount any weapon he wanted. If he chose to, he could obliterate an entire planetary system into fragments in short order—

—and with more than just one method.

Photoids were merely the simplest and cheapest option.

”Commander, I just realized you now have way too many ways to destroy stars?!”

Gudako, beside Setsuna, counted them off on her fingers.

Even though the Trisolaran universe was only sub-light level, they had undoubtedly created all sorts of absurd things here.

”Mhm, each has its strengths and weaknesses.”

Setsuna reviewed his arsenal.

Currently, the Eternal Snowfall possessed three methods of star-destroying attacks:

Fallen Star Lance, Photoids, and Dual-Vector Foils.

The Fallen Star Lance provided ultra-long-range instant strikes. Within hundreds of light-years, the moment it fired, the target star system was finished.

No reaction time, virtually no defenses, and with overload mode, its destructive power could be pushed even higher.

Its only drawback was the massive energy cost and the need for pre-charging.

Photoids were the simplest, cheapest, and most convenient. But since they traveled only at sub-light speed, clearing out a large stellar system might not completely annihilate the enemy.

Otherwise, the Singer in the original story wouldn’t have abandoned photoids for dual-vector foils to strike the Solar System.

Over long distances, photoids could theoretically be intercepted by lightspeed or FTL civilizations.

They were best for bullying natives, or for attacking enemy fleets at medium and close range.

Dual-vector foils were also sub-light weapons, with devastating power. Few civilizations had any means of resisting them. Even most FTL civilizations could only flee.

Their kill range was massive. Left unchecked, they could wipe out an entire galaxy.

Their drawbacks were the same as photoids—too slow. And the contamination was too severe. Until controllable dimensional strike weapons were developed, they couldn’t be used recklessly.

The foils captured from the Singer, along with the newly manufactured ones, were all stored under Setsuna’s control.

No one was allowed to use them without prior approval.

Tossing them casually was nothing like the shipgirls playing around with photoids.

”….”

”Tch, Commander, you’re so stacked with weapons now. Can’t you do something to make me stronger too?!”

Gudako suddenly pounced on Setsuna’s back, puffing her cheeks and acting spoiled.

”Look at you—you’ve got three different ways to crush a sun, and I’m still just swinging a hammer?!”

”Help me out here!!”

She pinched Setsuna’s cheeks, pouting like a sulking girlfriend.

”When you piloted Strike Freedom, I was still in Barbatos, swinging my hammer.”

”When you took command of the Eternal Snowfall, I was still in Barbatos, swinging my hammer with magic buffs.”

”Now you’ve become the Juggernaut, and I’m still in Barbatos, swinging my hammer with twenty-eight types of spells and enchantments!”

Setsuna laughed angrily and flicked her forehead.

”When I handed out Teigu and magic scrolls, did I ever skip you? All that equipment in your pack is fake then, huh?!”

”That’s different! You all can smash suns now, while I barely scrape the surface of planets.”

Gudako glanced at the shipgirls, full of envy.

Every time they visited a new tech world, they got to feast and thrive alongside the Commander.

Now, even the tiniest loli destroyers had star-level destructive power.

Ridiculous. Absolutely ridiculous.

”….”

”Gundams can only be modified so far. How about I give you a starship instead?”

Setsuna asked.

”No! I don’t have your trick of summoning and dismissing rigging. What would I do with a ship?”

”Uh…”

”Then I’ll scout the star charts when I have time. Maybe we’ll run into another Gundam world. I’ll get you a stronger unit as soon as possible.”

Setsuna considered.

Her Gundam form hadn’t changed for a long time, basically just receiving technical upgrades alongside the starships.

After entering the space age, most of the time it was hardly needed at all.

”Oh, there are still two more magic worlds ahead. You should be able to learn a few things there. Or maybe I’ll get you a Divine Key in the future?”

”Yay!”

Gudako’s eyes sparkled with joy at the big promise Setsuna drew for her.

”I will go through fire and water for you… no, I will even offer myself without hesitation!!!”

Whack!

Richelieu chopped her with a hand strike.

”Offer yourself? There’s a line for that, you’ll have to get a lottery number!!”

...

After the shipgirls had all changed into their new equipment, their combination of FTL starships plus photoid strikes drastically accelerated the pace of clearing out alien civilizations.

Sensors were activated to scan the surrounding star regions.

Whenever an alien civilization was discovered, they would head over, destroy the enemy fleet, capture a few prisoners for research—

—and then finish with a photoid strike to eliminate any future threat.

In just over a month, not only within 200 light-years, but within a radius of 500 light-years, nearly everything had been turned into an empty zone.

Meanwhile, the dimensional research teams, escorted by shipgirls, carried out terrifying experiments in various sectors.

...

Deneb (Alpha Cygni), 3,200 light-years from Earth.

In the Stellar World, this was the homeland of the Human Federation. But in the Trisolaran universe, it was nothing but emptiness.

”The sixteenth controllable dimensional reduction strike experiment—begin!”

Observer, Purifier, Compiler, and Daedalus stood upon a barren planet, tinkering with a gigantic machine shaped like a turret.

Around them were a few escorting shipgirls, and the Abyssal sisters from the Northern Union.

Little Northern was being led by Harbor Princess and Central Princess , happily licking a lollipop.

They too were responsible for guarding the researchers.

The three Siren girls rapidly calculated data on the holographic interface, while Daedalus finished her adjustments.

The turret was aimed at Deneb.

Boom—

A deep rumble echoed.

An invisible, forcefield-contained two-dimensional space was launched at sub-light speed, striking the star.

The dimensional reduction of a star was a spectacular sight.

The distant sun’s brightness surged. At the instant it touched the two-dimensional plane, it melted downward, flattening into a circular sheet that rapidly expanded.

It became a vast sea of fire.

A massive oval, its core blazing brilliantly. Surrounding layers—the radiation zone, convection zone, photosphere, chromosphere, and corona—were all projected clearly across the enormous sheet.

”Whoa…”

The escorting shipgirls stared blankly.

Observer and the others, however, were frantically calculating.

Suddenly, they realized—

After the star collapsed into two dimensions, the dimensional space did not stop expanding. Nearby planets began to fall into it as well.

”Crap, the experiment failed! Retreat!!”

Purifier shouted.

Shwoom—

The Sirens manifested their ship forms. As members of the port faction, when the shipgirls had been upgraded, they too had gained FTL engines.

Harbor Princess and Central Princess tossed the experimental device and Little Northern onto the ship.

Boom—

The starships activated their FTL drives, vanishing into the night sky.

”Hiss… was there a parameter error in the spatial design? Daedalus, tweak it. Let’s try the Beta plan.”

Purifier analyzed data while poking at her colleague.

After a quick discussion, the researchers had a new experimental plan within minutes.

The blueprint was handed to the Bulins, who immediately started hammering away on the starship to refit the device.

”Next experiment site… Gamma Cygni, 600 light-years away. Depart!”

The little Observer marked a location on the starmap, and the group moved on.

Researching dimensional reduction weapons was extremely dangerous. If the experiments failed, they created uncontrollable two-dimensional spaces like dual-vector foils.

Three-dimensional space would collapse without end.

Thus, such experiments could only be carried out in this universe.

With FTL ships, experiments could be conducted across countless star systems of the galaxy.

”Speaking of which… if we keep doing this, won’t the Solar System eventually fall into two dimensions too?”

Purifier suddenly thought of something.

”Relax. The closest experiment site is 3,000 light-years from the Solar System. That’s 3,000 years! If we still can’t develop controllable dimensional reduction tech by then, we might as well all go two-dimensional together.”

”We’ll definitely be done with the research and gone by then.”

Observer replied nonchalantly.

”What about the humans there?”

Daedalus, kinder at heart, asked.

”Well… for now they’re behaving themselves. If they keep doing well, maybe the Commander will send them off to vassal worlds to work.”

The little loli thought for a moment.

”If they don’t behave… well, their ending will probably be the same as in the original storyline.”

”Oh.”

The others nodded.

”Other alien civilizations are the ones who’ll suffer.”

”Doesn’t matter.”

Observer tapped the console with her tentacle rigging.

”When an elephant walks down a path, does it care how many ants it steps on?”

”…True.”

...

”United Earth Government, subdued and under review.”

”Trisolarans, dealt with. Sophon technology acquired. Droplets, no application value.”

”Singer, eliminated. Gained photoid and dual-vector foil manufacturing tech.”

”Photoid strikes fully deployed. Controllable dimensional reduction research underway…”

On the Eternal Snowfall’s bridge, Setsuna leaned back in his chair, crossing off one item after another on the holographic interface.

Though their stay in the Trisolaran world hadn’t been long, the harvest was undeniably abundant.

Sophons that could unfold in higher dimensions, convenient photoid strikes, and the terrifying dual-vector foils.

All the familiar and useful technologies had been secured.

As for controllable dimensional reduction, he was certain no civilization in this universe had achieved it. That would have to be developed by themselves.

The Starsea Empire’s foundation in science was already more advanced than the Trisolaran world’s, so he remained optimistic.

Of the planned objectives before departure, more than half were complete.

Calculating it all, only a few ”background pieces” remained, yet to be encountered or obtained:

The Zero-Homers.

Pocket-universe creation technology.

And the rumored weapon said to be wielded only by gods—”Mathematical Laws.”

The ”Zero-Homers,” also called Resetters, were one of the god-level civilizations of the Trisolaran universe. They believed the eleven dimensions of the cosmos cycled in succession, like a clock hand passing twelve and returning to zero.

Thus, to resolve the collapse caused by rampant use of dimensional reduction weapons, their goal was to reduce the entire universe to zero dimensions, then let it cycle back up through to ten dimensions.

Ultimately, the universe would ascend to higher dimensions again, effectively rebooting itself.

It sounded almost like performance art.

Whether their theory could succeed was unknown, but their technological level was undoubtedly among the very top in this universe.

Comparable perhaps to the civilization from the original story that broadcast across universes with supermembranes.

Among the natives, they were some of the strongest, surely holding all manner of strange technologies.

”When you were patrolling, did you ever encounter a ’death line’? That wake left by a high-output lightspeed ship?”

Setsuna asked across the fleet comms.

”Nope, never seen it.”

The shipgirls shook their heads.

”Tch, a pity.”

”Maybe Earth is just too far from the galactic center—like some backwater countryside?”

Setsuna snorted.

He really wanted to meet this universe’s godlike civilization. The Trisolarans, the Singer—none of them counted as particularly strong among the natives.

Unfortunately, the few thousand light-years he had explored were but a drop in the cosmic ocean.

After pondering for a while, a thought came to him.

”If they won’t come find us… maybe we should go out and look for them?”

”Little Grey.”

”Hm?”

The nanobot’s avatar appeared on the holographic screen.

”I want to find the Zero-Homers Alliance. Any ideas?”

”Uh…”

Little Grey thought for a moment.

”Build a Sentry Array?”

”You’re asking me to construct a galactic wonder in the Trisolaran universe?! Do we even know how?!”

”Broadcast a signal across the universe?”

”That’s a good idea. Anything else?”

Setsuna noted it down.

”Uh… there’s also a simpler way: I could turn into a Grey Goo storm and carpet-search the galaxy.”

”???”

”You want the sub-light natives to face a Stellaris-style crisis?!”

—

—

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