Crossover Shipgirls: Building a Dimensional Empire from Scratch

After Grey’s Western King-style governance, Earthlings were completely subdued, with no more troublemakers causing disturbances.

The nanobot’s reputation as one who could even stop children from crying at night had spread throughout the fleet. Everyone decided that if they encountered any more difficult troublemakers, they would just hand them over to Grey.

Setsuna’s attention returned once more to the exploration of the Trisolaran universe.

Within a radius of 200 light-years, he had marked out a security zone for the Solar System’s starbase.

The shipgirls divided into several fleets, spreading out in all directions for a carpet-style search.

The Eternal Snowfall remained stationed in the Solar System, ready to provide long-range strike support for the expeditionary forces at any time.

At this moment—

Everyone once again directly witnessed the Juggernaut’s power of extinguishing stars and shattering suns.

”Commander, in the Eridanus Zeta system, we discovered a spacefaring civilization.”

”They appear to be some kind of reptilian species. They have two colonial systems. We have already destroyed their space fleet and captured some of their kind to bring back for study.”

Essex transmitted the coordinates to Setsuna.

Three points were clearly marked on the star map.

In the Trisolaran universe, most weak space civilizations followed the Dark Forest law, concealing their homeworlds.

Unfortunately, such concealment was useless against FTL detectors.

”Received. Fallen Star Lance is ready. Stay clear.”

”Understood.”

The Eternal Snowfall’s massive hull slowly turned.

It locked onto a star system ten light-years away and began charging.

—Boom!!!

A crimson energy beam split the cosmos.

On the other end of the starlit void, a star shattered and exploded, reducing everything within that system to dust.

”Target eliminated.”

”Proceed to the next star system strike, Eridanus Alpha, coordinates are…”

The blinding brilliance of the Fallen Star Lance continued to pierce the darkness of the universe.

Each shot meant another star extinguished in the sky, another civilization destroyed.

”There are more civilizations in the Trisolaran universe than I imagined.”

Setsuna sighed as he looked at the continuous reports.

He counted. In just half a month, the number of destroyed civilizations had already reached double digits.

Unlike his own main world, where within several thousand light-years there was nothing but emptiness, this universe was packed with civilizations.

It only seemed sparse because most civilizations deliberately hid their existence.

”Commander, should we consider developing a few vassal states here?”

”If we keep several space-age alien civilizations as vassals, the output should be quite profitable, right?”

Shoukaku asked.

”...”

Setsuna thought for a moment.

”No need.”

”For safety and stability, it’s better to invest in developing our existing vassal worlds. Those universes don’t have demons and monsters.”

”As for these aliens, their best fate is to perform circus tricks for us in the zoo or serve as research material in laboratories, mm.”

Most of the dozen or so vassal civilizations had been uplifted from primitive stages into spacefaring humanity and respected their suzerain greatly.

Developing their universes alone provided more than enough resources.

This universe, however, was a chaotic battleground.

Low-level civilizations schemed against one another with the Dark Forest law, while high-level civilizations threw dimensional strikes, using law-based weapons to riddle the cosmos with holes, ultimately dragging everyone into destruction together.

It was better to finish researching their technologies quickly and leave.

”Oh…”

The shipgirls nodded in vague understanding.

For them, enjoying the long-awaited interstellar war was the fun part. After becoming starships, they finally had a chance to shine again in the void.

As for matters of development, they gave it little thought.

Frontline shipgirls continuously sent back battle reports.

”Commander, Eagle Union First Fleet, near Cetus UV star, eliminated 256 alien ships, captured one flagship. They were aquatic creatures.”

”Their homeworld is an ocean planet… Oh oh oh oh, the submarine shipgirls dove in and beat them up!!!”

”Comrade-chan, in Ophiuchus Beta, the Northern Union Fleet discovered an alien civilization. Hmm, their government seems like a giant corporation… let them taste the Soviet iron fist, Ura!!!”

”Near Sirius, a lightspeed ship trail was found. The Sakura Empire Second Fleet is pursuing it…”

The endless reports dazzled the eyes.

Setsuna felt that the expeditionary shipgirls seemed to be having a lot of fun, gleefully bullying sub-light natives in all sorts of ways.

”Tch, all the others already hogged the targets. Commander, isn’t there a stronger or more interesting opponent we can take on for some fun?”

Formidable lay sprawled on the Eternal Snowfall’s sofa, pouting at Setsuna in a spoiled tone.

After they had beaten up the Trisolaran fleet, she and her sisters had been stuck in the Solar System, on standby as a mobile unit.

All they could do was watch the others fight.

”Zzz…”

Implacable lounged on another sofa, pretending to nap.

”If only everyone else could finish the job… Zzz…”

”Let me rest a bit… Zzz…”

”Tch, with that attitude, no wonder the Commander never invites you to his parties.”

Formidable rolled her eyes.

”???”

Even half-asleep, Implacable caught wind of something outrageous.

”After we clear out the 200-light-year radius, we’ll explore farther. By then, we’ll run into stronger civilizations.”

Setsuna replied casually.

He was scanning the incoming battle reports when—

Suddenly.

A new message cut in.

It came from the Sakura Empire Second Fleet, which had a mixed complement of Kancolle shipgirls.

”Commander, we’ve found a dangerous target, poi!!”

Yuudachi’s head popped up on the holographic screen.

”A lightspeed ship is approaching from 200 light-years away, and on board there’s an alien who loves singing, poi!!!”

”And his singing is suuuper awful, poi!!!”

”Hah?!”

...

200 light-years beyond the Solar System.

A spaceship streaked through the void at lightspeed, leaving a glowing trail across the nebulae.

”I see the one I love, I fly to her side.”

”I bring her a gift, a little fragment of frozen time,”

”Time with beautiful stripes upon it…”

The Singer hummed ancient ballads within the ship, while scanning his surroundings.

When this seed ship had set out from the homeworld, it had still been a place of joy.

But later, ever since war broke out between the homeworld and the fringe worlds, that joy had gradually faded.

In the olden days, joy had been etched into the ancient ballads. Singing them was one of the few pleasures left now.

As a lowly janitor of the homeworld, the Singer’s task was simple.

Hide himself well, and perform ”cleaning.”

To ”clean up” any civilization that exposed its coordinates.

Not just by observing with the ship—sometimes other civilizations transmitted coordinates, broadcasting them aimlessly.

The ship could capture and analyze such coordinates, then locate the corresponding world.

Coordinates with sincerity, coordinates without sincerity.

Coordinates without sincerity often pointed to empty worlds. Cleaning such voids wasted energy, and worse, sometimes it was harmful, because empty worlds might still be useful later.

This ship’s course lay along the edge of the Orion Arm, on the galactic outskirts, where few civilizations resided.

None strong like the homeworld.

—Or perhaps strong ones existed, but had hidden their homeworlds.

”A destroyed world?”

At that moment, the Singer noticed a strange star system in the distance.

Its sun had been shattered completely, collapsing into a small black hole. Everything in the planetary system had been torn apart by the stellar explosion.

Now interstellar debris circled the accretion disk.

Judging from the still-cooling planetary cores, the system’s destruction wasn’t long ago.

”Someone already cleaned this place?”

”Was it by mass-point?”

The Singer wasn’t surprised.

In the universe, no matter how fast you were, someone was always faster. No matter how slow, someone was always slower.

It was normal for someone ahead of him to have cleaned away unknown civilizations.

He activated a ship process, archiving the data.

At the same time, he began analyzing the source of the strike.

Normally, such analysis yielded nothing—strikers usually hid themselves well.

But this time, the ship’s main core quickly flagged an anomaly.

”It was just cleaned?!”

The main core’s analysis concluded the system had been struck less than one day ago.

That meant the attacking ship might still be nearby—making it highly likely they could be tracked.

He activated a process of the ”Big Eye,” trying to pinpoint the source.

”What are you doing? The Big Eye is busy.”

The Seed’s Elder asked.

”I located a destroyed low-entropy world. The cleaner hasn’t gone far.”

The Singer replied.

”Oh, fine then.”

The Elder consented.

The ship gradually slowed.

The Big Eye analyzed the destruction in detail.

Soon.

The onboard 5.9 AI produced a shocking conclusion.

The star hadn’t been shattered by photoid strikes. It had been destroyed by an intense high-energy blast.

Like lasers, plasma, or some other unknown weapon tearing apart its outer shell and core, triggering a catastrophic explosion.

In the universe, this was an extremely uneconomical method of cleaning—one that easily exposed oneself.

”A new method of cleaning low-entropy worlds? Strange.”

The Singer dug deeper.

...

Minutes later.

He froze at the Big Eye’s data.

He had witnessed something more terrifying than a dimensional strike.

The blow had come from hundreds of light-years away.

Yet the moment the attack occurred, the star was shattered instantly, leaving no time for precise tracking.

This strike violated the laws of this world.

”Elder, there’s a situation.”

”The cleaner is much faster than us.”

The Singer said.

”You mean they arrived long before us?”

The Elder asked.

The ship resumed lightspeed to continue its journey.

”No. I mean their ships are faster than ours.”

...

Shwoom—Shwoom—

The glow of the warp engines flashed across an unfamiliar star system 200 light-years from the Solar System.

The colossal Eternal Snowfall, vast as a planet, tore through space and descended into the void.

On the holographic display, a special target was marked at a distance of one light-year.

It was a lightspeed ship, heading toward the Solar System.

According to the original Trisolaran timeline, the Solar System was struck by dimensional reduction in the 67th year of the Bunker Era, that is, the year 2405.

The Singer’s ship had, a few years prior, passed the edge of the Solar System, tossing a dual-vector foil at the outer rim of the Oort Cloud.

Setsuna had crossed over during the Crisis Era, just after the Doomsday Battle.

That was roughly two centuries before the dimensional strike would have occurred.

Now, the Singer’s ship was 200 light-years away, heading toward the Solar System.

”Based on its trajectory, if it doesn’t decelerate, it will reach the outskirts of the Solar System in about 193 years.”

”At that time, it will be able to directly observe the situation inside the Solar System, as well as the destruction of the Trisolaran system.”

The ship’s AI simulated the vessel’s course.

”So it looks like setting the security zone at 200 light-years was perfect timing, huh?”

The shipgirls crowded around. At first, they had thought Setsuna had just picked a random range.

”So this is the Singer? The bastard who used the dual-vector foil to reduce Earth into a lower dimension?”

Several little shipgirls studied the holographic projection of the vessel closely.

With a distance of one light-year, it was perfectly safe. The Singer couldn’t possibly detect them.

Through precise sensor scanning, the structure of that ship was projected in detail onto the Eternal Snowfall’s main console.

Its design was vastly different from the Trisolarans, carrying strange and twisted concepts beyond human comprehension.

Among the scans, the ship’s AI highlighted certain stored ”hazardous items” that emitted unusual energy signatures.

”The Singer is a janitor of the homeworld. They release seed ships that travel along predetermined routes, cleaning up any civilizations that expose themselves.”

”Sometimes they use photoids—the Singer calls them mass-points. Other times, they use dual-vector foils, the very same weapons meant to destroy the Solar System. Those are the most devastating weapons of the Trisolaran universe.”

Setsuna glanced at the scan results.

The seed ship carried many photoids and dual-vector foils. Who knew how many civilizations the Singer would wipe out in a single voyage.

According to its own timekeeping, the seed ship had already been traveling for over ten thousand time-grains—that was about seventy thousand years.

The number of civilizations it had destroyed must have been immense.

”Hiss… That ship may be a bit outdated, but it looks extremely dangerous…”

Formidable twirled her hair.

A ship loaded with dual-vector foils was practically a suicide truck.

Even if it couldn’t hurt FTL warships, it could still contaminate the environment severely.

—And such contamination had no cure.

The greatest strike in the Trisolaran universe was dimensional reduction, collapsing the cosmos from eleven dimensions down to three.

Even countless god-level civilizations had failed to find a way to reverse high-dimensional collapse into lower dimensions. At best, they could preemptively descend and survive in a reduced dimension.

What the civilizations of the idyllic era couldn’t resolve, Setsuna certainly couldn’t fix now.

Governing the entire universe wasn’t realistic, so he thought of something simpler.

”Capture the Singer and its ship. Seize the photoids and dual-vector foils. Use them to study dimensional technology.”

At the order—

The starship shipgirls leapt from the bridge, manifesting their vessels and thoroughly scanning the surrounding starfield.

They confirmed no other targets were present.

”Maintain a one-light-year safety distance.”

”Nymph, prepare for electronic intrusion. We must paralyze the ship in an instant, stripping it of resistance to prevent a dual-vector foil self-detonation.”

Setsuna ruffled the little loli’s head.

He had realized that in interstellar warfare, the Angeloid’s role in electronic warfare had been amplified countless times.

”Heh, Master, now you see how amazing I am~”

The little loli enjoyed the head-pat, squinting happily, hands on her hips.

She even took the chance to flaunt her Commander’s affection to Ikaros and Astraea.

”One minute! Watch me take them down!!”

...

Inside the ship.

The Singer and the Elder fell into silence.

They had allocated all of the Big Eye’s threads to analysis, but the results remained the same.

The strike was instantaneous.

It had spanned hundreds of light-years, yet the moment the attack occurred, the star was destroyed.

An FTL strike.

This was a terrifying cleaner, one who had stepped outside the laws of this universe.

Far more terrifying than the homeworld’s enemies or the fringe worlds.

Because of constant defeats in war, the homeworld had already considered reducing their entire species into two dimensions, then recklessly unleashing dimensional weapons on their enemies.

But now, the Singer felt that perhaps the war between the homeworld and the fringe worlds was only a trivial part of this dark cosmos.

Somewhere in the stars, there existed a hunter beyond imagination—cleansing so-called advanced civilizations just as the Singer cleansed lesser ones.

”If the laws can be altered to lower lightspeed, or to reduce dimensions…”

”Then could there exist methods that let one surpass lightspeed?”

The Singer posed the question to the Elder.

”Impossible. If you exceed lightspeed, the entire foundation of science collapses. In theory, it’s—”

The Elder stopped halfway.

The homeworld was not the most advanced civilization in this universe. The ”laws” and ”science” they knew were only deductions within the existing framework of this cosmos.

If there truly existed a civilization far beyond them, one with a completely different foundational system of science…

”!!!”

The Singer and the Elder realized they had stumbled onto something monumental.

Countless possibilities flashed through their minds.

”Return!!!”

The moment the words were spoken—

The ship jolted violently, falling out of lightspeed.

Alarms blared everywhere.

Including the Big Eye, the entire ship’s weapon systems, engines, and AI were all hacked and paralyzed.

”Intrusion… into a lightspeed ship?!”

The Singer realized another horrifying truth.

Normally, no signal should be able to catch a lightspeed vessel.

Yet before the crew could even respond—

From the Eternal Snowfall, hundreds of carrier-based aircraft launched. Using short-range jump drives, they instantly crossed the one-light-year gap and appeared beside the ship.

Shwoom—

Each aircraft fired several missiles, which detonated at lightspeed right beside the target.

They were weapons similar to subsonic hydrogen bombs designed against biomass, devastating to organics—a type Grey particularly liked.

Their speed and power were orders of magnitude beyond anything aboard the Natural Selection or Blue Space. With near-range jump-bombing, evasion was impossible.

Vmmm!!!

The radiation streams of thousands of missiles pierced the ship.

All crew aboard were instantly reduced to pools of grey inorganic matter.

...

After confirming no further threats aboard—

The Eternal Snowfall opened its hangar and retrieved the ship.

The Angeloid and Grey began carefully dismantling and studying it.

The Singer’s civilization had already developed lightspeed ships, mastered dimensional strikes, and even the ability to descend into two dimensions themselves. Within the Trisolaran universe, they were considered above-average.

At the very least, they could drag the universe into collapse with dual-vector foils and survive as a two-dimensional species.

But the ship itself was unimpressive. A crude creation of natives, awkward for humans to use.

Yet, after only a few dozen minutes, Grey found what they needed.

”Here, Commander.”

”In the storage bay—there are dozens of them, all sealed in forcefields.”

She stood before Setsuna, opening her pale hand.

Resting in her palm was a pure-white strip, less than ten centimeters long and five wide. As thin as a sheet of paper.

Roughly the size of an ID card, with no thickness at all.

It didn’t react to any kind of electromagnetic wave—not even tachyons or luxons.

It was as if transparent, able to pass through any obstacle.

Only forcefields could hold it in place.

”Ohh…”

After Grey confirmed multiple times that the sealing was secure and there would be no accidental leaks, the shipgirls crowded closer.

A dual-vector foil.

The Trisolaran universe’s ultimate interstellar weapon. The culmination of law-based warfare. The very doomsday tool that had ended this cosmos.

Inside it was a sealed two-dimensional space. When the forcefield vanished, the surrounding three-dimensional space would collapse into two.

The collapse would accelerate, eventually reaching lightspeed.

Within hours, an entire star system would be reduced to two dimensions. Given enough time, the whole galaxy would fall.

Three-dimensional beings could not survive in two dimensions. It wiped enemies out completely.

A terrifyingly cool weapon.

”Ahem. Take it back for research. Strict regulation.”

Setsuna cleared his throat, accepting the dual-vector foil.

”Under no circumstances is it to be used in our own universe or vassal worlds!”

”Commander, I just thought of a very rude way to use it.”

Gudako suddenly raised her hand.

”Hah?”

Everyone turned toward the human menace.

”If there’s a world you don’t like, just use your authority to open a portal, toss a dual-vector foil through, and close it.”

”Then just wait for them to slowly die off.”

”Throwing cosmic trash around the multiverse?!”

Grey’s face twitched.

”...”

Setsuna was silent for a moment.

”…You really do come up with the wildest ideas.”

”I’m in awe of your imagination.”

—

—

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