Crossover Shipgirls: Building a Dimensional Empire from Scratch

The technologies obtained from the Three-Body world mainly included sophons, photoids, dual-vector foils, pocket-universe creation, and law manipulation.

After the widespread use of sophons and photoids, the research focus naturally shifted toward pocket-universe creation.

Half a month later—

Kayo Senju brought a few research lolis and Bulins to report to Setsuna.

”Commander, we’ve preliminarily grasped the method of pocket-universe creation and request to conduct an experiment.”

”That fast?”

Setsuna looked at the little lolis with some surprise.

In his impression, pocket-universe creation was something civilizations close to god-tier mastery could achieve only in the late stages of the Three-Body world.

It was essentially slicing off part of the universe’s matter to create an independent spacetime system.

Many civilizations sought to hide inside such pocket-universes to avoid two-dimensional reduction and destruction of the universe.

”Creating a universe.”

Just hearing the concept alone was enough to know it was an extremely complex undertaking.

”Uh…”

”To be precise, we only understand the principles of pocket-universes from a popular science perspective. As for the detailed technical processes, we don’t quite get them yet.”

”It involves dimensions of space, spacetime manipulation, and many other areas we’ve never researched before. Everyone’s still learning.”

The little loli scratched her head in embarrassment.

”It will probably take two or three more years to fully master this knowledge.”

For the research lolis to reach god-tier civilization technology within just a few years was already a mark of their extraordinary brilliance.

But the shipgirls were more curious about something else:

”If you haven’t learned it all yet, how did you build a pocket-universe?”

”…”

Kayo Senju’s face flushed. After holding it in for a while, she admitted awkwardly:

”The data on pocket-universe creation given by the Zero-Homers included detailed blueprints and design schemes. Their language is very complicated, and their design concepts are strange. We had some trouble understanding…”

”So I showed it to a Specialized Bulin…”

”And then the Bulin said she understood it.”

”?”

One of the Specialized Bulins raised her hand.

”Bulin thinks she can build it, buli!!!”

”…”

The research lolis looked somewhat defeated. After all their hard work pulling all-nighters studying literature and data, they were still outdone by a Bulin’s sudden flash of inspiration.

It was like a professor spending ten years researching controlled nuclear fusion without success—only for some random green-skinned passerby to glance at it and say, ”I think you can just do it like this,” and the problem was solved.

”Oh, impressive.”

Setsuna ruffled the Specialized Bulin’s hair.

”So we want to let the Bulins try to make a pocket-universe. Then we’ll research the finished product. That should speed things up.”

”And in the future, we can also improve its flaws.”

Kayo Senju suggested earnestly.

”Alright.”

Setsuna agreed without hesitation. He was also eager to see pocket-universe creation technology firsthand.

Though Bulins were strong, what they created was only according to specific blueprints.

Going further would depend on whether the research lolis could adapt the technology into something they wanted.

”Tell me what you need.”

He waved his hand.

”Mhm…”

Kayo Senju pulled up a list on the holographic interface.

”A pocket-universe is an independent spacetime system apart from the universe.”

”It’s like blowing a bubble on the edge of the universe’s space. This bubble universe becomes separated from the main one, forming a smaller, independent bubble.”

The technical details were far too complex for Setsuna and the shipgirls to follow, so the little loli explained in simpler terms.

”So, it’s like creating a little bubble-world?”

Setsuna asked.

”Mm… that’s one way to understand it.”

Kayo Senju nodded.

”Everything inside the bubble is independent of the outside. Even if the universe is destroyed, as long as the bubble’s matter is sufficient, it can continue to exist.”

”In the Trisolaris universe, so many civilizations wanted to use small worlds to escape the collapse and two-dimensionalization of the universe, returning to the pastoral age—that’s the reason.”

Genesis.

Setsuna could only think of this one word.

Artificially creating an independent spacetime pocket-universe—this was the power of god-tier civilizations.

”Mm, there’s another matter. The materials to build pocket-universes can only be drawn from the universe. The larger the bubble-world created, the greater the consumption.”

A research loli continued explaining.

”For example, to create a pocket-universe the size of Earth, the consumption would be about the resources of 5–6 Earths.”

”To make a solar-system-sized pocket-universe would cost the equivalent of 5–6 solar systems’ resources, including their stars.”

By size classification, pocket-universes could range from city-level, nation-level, continental, planetary, and up to star-system scale.

The smallest one recorded was Universe No. 647 from the original story, where Cheng Xin lived. Just one kilometer square, it consumed around 500,000 tons of matter according to Sophon.

Larger pocket-universes required several times more matter than their intended volume. Below planetary size it was manageable, but once reaching star-system scale, the cost was absurd, requiring the consumption of multiple stars.

”The largest recorded was galaxy-scale. To create a Milky Way-sized pocket-universe would consume the resources of several massive galaxy clusters.”

”As for higher tiers, even the Zero-Homers had never built them.”

Kayo Senju read from the data.

”Oh…”

A galaxy-sized pocket-universe sounded astounding, and the shipgirls were full of awe.

Gudako raised her hand, connecting the dots:

”Since we have so many vassal worlds, couldn’t we drain a few universes and build a bubble-world as large as the real cosmos?”

”???”

Kayo Senju froze for a moment.

”You have imagination. Theoretically, yes—if we had enough resources, we could build a one-to-one scale new universe.”

”But I really can’t picture a method to drain an entire universe’s resources. Even with FTL, developing a whole cosmos is incredibly difficult…”

”I know! The Commander taught me.”

...

Gudako spoke confidently:

”Fishing can never empty a pond of fish. To be efficient, of course you use a pump to drain it dry—in this case, an ether-phase device…”

Thump—

Setsuna stopped Gudako’s endless imagination and brainstorming.

Building a universe of equal size was certainly appealing and cool.

Inside a pocket-universe, every parameter could be self-defined—essentially becoming its master.

But food had to be eaten one bite at a time, and roads walked one step at a time.

”Let’s start with a city-level pocket-universe.”

He thought it over.

A planetary-level one would consume several planets’ worth of resources—unnecessary for now.

For the first attempt, experimentation came first.

Shwoosh shwoosh shwoosh—

Setsuna approved the resource expenditures the research lolis requested.

”Understood.”

The little lolis and Bulins left cheerfully.

Faintly, their chatter could be heard:

”Bulin, Bulin, can you really make a small world?”

”Of course, Bulin has completely understood, buli!!!”

”Then how will you cut space from the universe?”

”With Super Meow-Meow No.1, burin!!”

”…Then what about the mirror devices for the pocket-universe?”

”Still with Super Meow-Meow No.1, buli!! My hammer is the hammer that crushes stars, kya!”

”…”

”Can I try using your meow-meow hammer?”

”Bulin thinks you wouldn’t know how! Ba—ka!!!”

”…”

Setsuna and the shipgirls exchanged looks.

The combination of research lolis and Bulins was cute, hilarious, and powerful.

...

After sophons fully took over administrative work, both Setsuna and the shipgirls noticed they had far fewer tasks.

Productivity was completely liberated by artificial intelligence—no more tedious daily data analysis.

All they needed to do was set a general direction periodically, and the details would be neatly managed by sophons and Angeloids.

Life became highly routine.

In the mornings, after breakfast served by the Royal Maids, Setsuna would conduct a routine patrol around the capital.

Some little lolis were still attending classes. Depending on their progress, even the slowest had begun middle school-level courses. Soon, large numbers of research lolis would join the workforce.

With three million high-quality scientists, they could support all the research needs of an interstellar empire.

Beyond the academy district was the residence of the Horse Girls.

The uma musume studied basic knowledge while continuing their training.

They had little direct connection with the empire’s development—unable to build ships, conduct research, or fight wars.

But whether Horse Girls or Catgirls, they were undeniably part of this nation.

”Trainer—ah no, Commander!”

On the training grounds, Special Week, Silence Suzuka, and a few others saw Setsuna, stopped their running, wiped sweat, and ran up.

”Commander, long time no see.”

”Mhm, I heard you went to another universe to fight aliens recently?”

Special Week’s ears twitched as she asked.

They knew nothing of interstellar war, imagining it only from what shipgirls said or what little information spread.

”It must have been tough, right? I’m just glad you came back safe…”

”I have no talent beyond running. I can’t help you, I’m sorry…”

Silence Suzuka lowered her head as she spoke.

”It’s fine. As long as you’re living happily here, that’s enough.”

Setsuna patted her head.

”Fighting is left to those skilled at it. You just do what you love.”

”You’re part of the Starsea Empire. There’s no need to belittle yourselves.”

”Mhm… thank you.”

Silence Suzuka nodded softly, then raised her head, eyes carrying a trace of hope:

”Um… Commander, could you watch my next race in person?”

”I want to show you the results of my training here.”

After staying at the base so long, she felt more and more that Setsuna was someone she could only look up to.

Whether shipgirls, dragon girls, Heroic Spirits, or Spirits—they were all far stronger than her.

Even trying to get closer to the Commander, she didn’t know how.

All she could rely on was her one talent: running.

”Sure, I haven’t really watched a horse race before.”

Setsuna smiled and agreed, then pulled out a crate of carrots.

”Here—premium space carrots grown at the starbase. Enju Aihara said they taste ten times better than those on Earth. I can’t tell the difference, so you have them.”

”Think of it as nutrition before the race.”

”Waa—”

Special Week’s eyes sparkled as she happily accepted.

”Thank you, Commander!!”

The Horse Girl gave him a warm hug, her tail wagging like a puppy’s.

”…”

”Commander’s getting more and more natural at charming girls, tsk tsk.”

Gudako clicked her tongue in admiration.

His ability to casually max out favorability was astounding.

”What you really mean is: why isn’t he charming me?”

Formidable delivered a critical hit without hesitation.

”???”

After completing his daily patrol around the capital—

When free, Setsuna would visit other planets or star systems.

Everywhere in the Solar System and its surroundings—except gas giants—Bulins and Angeloids could be seen.

They were building small colonies and industrial zones, steadily expanding the empire’s borders.

In this universe, devoid of alien rivals, there was no competition for resources. They could simply farm and grow at leisure.

At night, depending on mood, Setsuna decided whether to visit shipgirls in the port, or spend time with Heroic Spirits, Spirits, or dragon girls.

Or gather everyone on the Eternal Snowfall and distort time for a few days of fun together.

A month passed quickly.

One day, in the Azur Lane port—

Setsuna was tangled up with the Illustrious sisters, wondering whether to give his lazy little sister Indomitable a few more rounds of IV therapy, when news arrived from the starbase.

”Commander, we built our pocket-universe!!!”

...

After the starship descended above the starbase, they boarded a shuttle and traveled to the research district.

There, Setsuna and the accompanying shipgirls met an excited Grey, Kayo Senju, and the proud-looking Bulins.

”Commander, I swear, this is the greatest invention I’ve ever seen…”

”Those sub-light primitives of the Three-Body world actually had some tricks up their sleeves in space and dimensional science, tsk tsk…”

Grey grabbed Setsuna and pulled him straight to the experimental plaza.

On the empty platform, aside from piles of engineering equipment and raw materials, there was almost nothing else.

”Pocket-universe? Where is it? Isn’t it supposed to be city-sized?”

Yukikaze peeked around curiously.

”The pocket-universe’s spacetime is independent from ours. You can only see its entrance, not its whole form.”

”Unless you can break into higher-dimensional space… well, maybe sophons could see it.”

Grey lifted a remote-control-like device and pressed a button.

Whoosh—

A strange object rose from the ground.

It was a rectangle traced out by faint glowing white lines, like a door about human height, floating in midair.

The lines were thin and dim. Against the cosmic black background, it was hard to notice.

Using sensors to scan, however, revealed intense spatial distortion around the ”door”—so extreme it defied explanation.

”Oh! Just like in the books!”

Yukikaze and Tashkent bounced excitedly, trying to rush inside.

But they passed right through and landed dumbfounded on the other side.

”I haven’t added your data to the recognition system yet.”

”Without permission, you can’t enter the pocket-universe.”

Grey chuckled…

After a moment of operation on the holographic panel…

”Alright, let’s go.”

Setsuna and the shipgirls passed through the transparent door.

Chaos and darkness.

For an instant, he felt exactly as when a ship engaged its warp drive—a vacuum of time.

There was no time here. Only when he entered did time begin to flow.

It felt like a second and like billions of years all at once.

The darkness gradually faded, and a sun lit up the sky.

They stood on a hill.

Below lay a small city, about the size of the capital’s satellite city, comparable in area to ancient Chang’an.

The city was neatly planned, clearly modular in design.

Some Bulins and Angeloids were working, constructing industrial zones and residential blocks.

In the distance stretched farmlands reaching to the horizon. Freshly tilled, not yet sprouting crops, with little yellow chicks tilling and fertilizing.

Looking up, they saw a blue sky overhead—just like the capital in its early days of construction.

Turning back, the entrance had vanished without a trace.

Looking to either side or behind, they saw the same city again, like a mirror image.

Even their reflections stood there.

Yukikaze waved, and the mirror Yukikaze waved back.

She made a funny face, and the mirror did the same.

”Oh?!”

The group followed the streets forward.

At the city’s edge, taking one more step forward carried them straight into the mirrored world.

Looking around—they were back at the starting point.

”Whoa?!”

The little shipgirls and Spirits who had come along gasped in awe, stunned by the ingenious design.

In this space, no matter which direction you walked, reaching the edge would bring you back to the beginning.

It was like a room with four walls, a ceiling, and a floor.

But here was the strange part: the ceiling was also the floor, and of the four walls, each opposing pair was actually one. In essence, there were only two walls.

If you walked from one wall toward the opposite, once you reached it, you instantly returned to the first wall.

”This is Misner space. Amazing, right?”

Grey explained with a smile.

”This is a universe. Though only city-sized, its principle is the same as a real cosmos.”

”It has independent space and spacetime laws. Even most physical constants can be adjusted.”

”Um, is it like the ’cave heavens’ in novels?”

Tashkent raised her hand. It felt similar to those mystical pocket realms described in stories.

”Much more advanced.”

Kayo Senju replied.

”The bubble-universe exists independently of the universe. Even disasters that sweep across the universe cannot affect it.”

”And its entrance can be carried around. If Commander wishes, he could mount many pocket-universes on a ship…”

—

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