Crossover Shipgirls: Building a Dimensional Empire from Scratch

Clack—

The installation of the miniature universes proceeded extremely quickly.

Because in essence, what they were doing was installing entrances onto the Eternal Snowfall. Their interiors were located inside independent world bubbles, separate from the main universe.

Colorful Bulins held Ultra Rainbow Hammer, hammering and tinkering across the hull of the Eternal Snowfall.

In the center of the bridge, a pale white ”door” was secured inside the main control room.

Inside the ship’s compartments, within the Juggernaut dock, and in many other sections, the entrances to the miniature universes were mounted onto the Eternal Snowfall.

”Now we need to link the connection between the miniature universes and the ship itself, anchoring them onto the Eternal Snowfall.”

Compiler sat within her mechanical rigging and tapped several commands across a holographic screen.

”Otherwise, they are merely independent extradimensional spaces. Even if their entrances are placed here, they would have no real association with the outside world.”

”To put it simply—even if you retract the hull, you still wouldn’t interfere with them.”

”Only after the two are merged into one can you truly control those universes, draw upon the energy of the miniature universes, or command this starship from within them.”

”Mm... we have never conducted an experiment like this before. Commander, you are the first. You will be an important experimental sample.”

The Siren girl’s expression remained blank, her tone calm.

This was the largest-scale modification in the starship’s history—placing sixteen worlds inside it.

”Please be sure to tell me your sensations and impressions. I will record every detail faithfully and use it for future research.”

”...Alright.”

Setsuna nodded.

From now on, the Eternal Snowfall would become the carrier of countless world bubbles. It itself would be a composite multiverse.

Though the universes were not large yet, they could be expanded gradually.

[Universe No.1 merged into the Eternal Snowfall.]

[Spacetime synchronization in progress... superstring spatial segmentation, 15%, 20%...]

[Universe No.2 merged into the Eternal Snowfall.]

[Spatial coordinate axis set to...]

Accompanied by the AI’s incomprehensible notifications, Setsuna unfolded the starship into higher dimensions.

Shua—

The six-dimensional Eternal Snowfall expanded to a terrifying scale, larger than the entire Starbase, nearly obscuring half the starry sky.

He discovered that the miniature universes were, in essence, high-dimensional spaces as well—only their dimensionality was even higher than that of his hull.

Within the six-dimensional environment, one could only see hollow void-bubbles. These were their projections into lower dimensions.

Each void-bubble represented a blank miniature world bubble.

Clack—

As the first void-bubble was placed into the starship, Setsuna felt something strange.

”It feels like something just got stuffed into my body.”

”???”

”Is this really the time for dirty jokes?!”

Gudako spat out a mouthful of water.

”Mm, I’m being serious. This thing is kind of big.”

”That’s enough, hey?! I’m watching the Eternal Snowfall’s modification with a serious learning attitude, okay?!”

”...Just tell me—does stuffing a small world inside count as big or not?”

The Engineering Division and the Siren girls directed hundreds of thousands of Bulins to carry out large-scale modifications on the Eternal Snowfall.

Each time a miniature universe was installed, the corresponding module had to be reconfigured.

The bridge section was planned as the Silver Garden—the party and residential area.

The core of the hull housed the largest miniature universe, to be used later for constructing Galactic Wonder and the ship-mounted Aetherophasic Engine.

The lower compartments would continue to function as docks. Through links with the miniature universes, the Eternal Snowfall would gain the ability to assemble Titans, planet-class warships, and even stellar-class warships.

Once assembled inside the miniature universe dock, they could simply be thrown out directly in battle.

Boom—Bang!!—

The starship twisted and deformed before their eyes.

Setsuna frequently used the Authority of Reason to assist the Bulins with their work.

More and more world bubbles were installed into the hull. From a high-dimensional perspective, they nearly filled the entire ship.

...

Several days later.

Clack—

[Universe No.16 has merged into the Eternal Snowfall.]

[Progress 98%, 99%, 100%.]

[World bubble integration complete.]

The final miniature universe was integrated into the hull.

Setsuna had been half-reclining in a chair, pretending to nap, when suddenly a small white-haired, golden-eyed girl’s face appeared before him.

”You’re awake?”

”The surgery was very successful. You’re already a girl now... ahem, no, wait—you weren’t asleep.”

Observer poked his cheek and opened a holographic interface.

”Mm... considering that the Eternal Snowfall’s capacity for these pocket realms—miniature universes—is also limited.”

”Without affecting the integrity of the hull, this is currently the maximum we can install.”

”A total of sixteen universes have been fully integrated into the starship. From now on, Commander, you can control sixteen small worlds. Mm.”

”Oh.”

”That’s it?”

Formidable, Illustrious, and the other shipgirls had gathered aboard the Eternal Snowfall, curious whether they might try this new technology as well.

”I thought such an incredible modification would take months or even years, like when we upgraded Juggernaut before.”

”Installing the miniature universes into the hull isn’t difficult. There’s still a lot to do afterward.”

Purifier led the way as everyone moved upward from the bridge.

At the end of the corridor stood a white ”door”—an entrance to one of the miniature universes, now part of the Eternal Snowfall itself.

Shua—

After stepping through, they arrived in a completely unfamiliar space.

The world was still shrouded in primordial darkness. Only the holographic dome above emitted a faint glow.

”We’ve only completed the basic structural framework of these miniature universes. We haven’t filled them with anything yet, so that part’s up to the Commander.”

”Right now, the Eternal Snowfall contains sixteen universes. Combined, the usable space exceeds a diameter of over a hundred light-years. How you use it is entirely up to you.”

Purifier floated in the air as she spoke.

”If you want to build megastructures, you’ll first need to open up a complete cosmic environment inside, then gather the Bulins to construct them slowly.”

Stellar megastructures required unimaginable resources and strict construction conditions. They could not simply be built out of nothing in the void.

”So we need to create a Genesis first, huh?”

Setsuna grinned.

”Yes. Sixteen worlds in total. Fully developing them will also be a massive project.”

”Mm... but the good news is that the flow of time inside the miniature universes can be adjusted. So relative to our time frame, it probably won’t take long.”

”Though the investment of resources and manpower can’t be reduced.”

The Siren girl answered.

”Mm...”

Beside him, Tiamat—who had been silently following Setsuna the entire time—gently poked him.

”We... create many... worlds?”

She did not understand the advanced technology, but after entering the miniature universe, the scene of darkness before creation felt very familiar to her.

”Yes. We’ll create Genesis together. This is perfectly within your specialty, isn’t it?”

Setsuna clapped his hands.

The Authority of Reason activated at full power.

Heaven and earth split apart. Chaos began to divide.

At first, a single point of light flickered in the distance. Within a thousandth of a second, it expanded into a blazing sphere of fire—a fiercely burning star.

A star was nothing more than a massive nuclear fusion reactor. In principle, it was simpler than constructing a starship—only requiring greater power.

Then several rocky planets formed around the star. Once captured by its gravity, they became part of a small planetary system.

”Oh...”

Everyone stared in shock at this world-creating miracle.

Tiamat wordlessly activated her Authority as well.

The Sea of Life manifested beneath her feet, spreading across the planets.

Flowers, grass, trees, birds, beasts, fish, and insects slowly emerged from the primordial sea.

In only a few hours, within the previously empty miniature universe, a planetary system nearly identical to the Solar System had been created.

Sunlight shone down. Life on the planets rapidly evolved. Primitive single-celled organisms iterated into early marine creatures, then left the oceans and moved onto land.

Birds and beasts filled the skies and forests. Even the planetary environment was reshaped.

There were lush tropical rainforests, endless grasslands, oceans covering half the globe, and even deserts along the equator and inland regions.

The climate was mild. The environment carried a primitive simplicity—like Earth before human civilization appeared.

They could dispatch an Angeloid legion to colonize it immediately without any issue.

”Creating Genesis together? What is this, some kind of Genesis power couple?!”

Gudako, along with the observing shipgirls and Heroic Spirits, was stunned by their seamless cooperation.

”Mm...”

Tiamat pondered for a moment. Rarely, she revealed a smile.

”Me... Master... hus... band and wife? Mm... I am happy...”

”No, no. I am... Mother!”

...

”Ahem. Then the overall construction of the Silver Garden is basically complete.”

Setsuna landed on the newly born planet, breathing in the fresh air.

Looking around, above him stretched blue skies and drifting white clouds, with a golden sun hanging high overhead.

If one went out into the wild, they could even see a sky full of stars.

Of course, that starry sky was merely a holographic projection within the miniature universe. The scale of Universe No.1 was only twice the size of the Solar System—not nearly large enough to contain too many planetary systems.

”Burin! So next it’s the Bulins’ job, burin?!”

A group of colorful Bulins descended noisily, crowding around Setsuna.

”Mm. Build a city on this planet. From now on, this will be the command center of the Eternal Snowfall.”

Setsuna replied.

”Burin! Understood, burin!”

”This planet is huge, burin!”

The Bulins hoisted their equipment and began surveying the area. As a world directly shaped out of nothing by Setsuna, this planet was enormous—several times larger than Jupiter.

Its terrain could also be molded freely. They could shape it however they wished.

Colorful Bulins manifested their rigging, pulling out all kinds of construction materials and equipment as they began surveying and selecting sites.

”Wow—”

Formidable, Taihou, Kanae, and the other girls who had come to watch were full of disbelief.

In less than half a day, this place had gone from nothingness and primordial chaos to a fully formed planetary system and ecological cycle under the Authority of Genesis.

And it would exist permanently.

Between the star and its planets, and the ecosystems upon those planets, a perfect cycle had already formed.

The Authority of Reason’s construction power and Tiamat’s Sea of Life were simply a match made in heaven.

”I feel like I’ve transmigrated again.”

Gudako and Formidable hopped back and forth near the ”door” of the miniature universe.

Taking one step backward, their vision blurred.

They stood once more on the bridge of the Eternal Snowfall.

Around them was silver-gray, sci-fi architecture. Through the viewports, they could see the Starbase and the vast sea of stars—this was the native universe of the Starsea Empire.

Taking one step forward, they crossed into the miniature universe’s door.

A sea breeze rushed toward them as they found themselves standing on a completely unfamiliar planet.

Before them stretched endless beaches and a deep blue ocean.

The air carried the briny scent unique to the sea, and seabirds occasionally cried as they soared overhead.

The stark contrast created a surreal illusion—as if a planet had been installed inside the Eternal Snowfall’s hull.

”You’re not wrong. The miniature universe is indeed installed inside the Eternal Snowfall.”

Setsuna checked a holographic interface.

”We’ll leave the subsequent construction here to the Bulins. Let’s go create the other universes.”

If he personally shaped every detail of each world, it would be far too troublesome.

Using the Authority of Reason together with Tiamat to sketch the broad framework of a world, then handing it over to the Bulins and Angeloids for detailed construction—this method was the most efficient and least exhausting.

”Burin, don’t worry!”

”The Bulins will build a super huge city here, burin!”

The Bulin foreman patted her chest confidently.

”Mm... We’ll turn this planet into an Ideal City, burin! The nearby moon can be a vacation planet, burin!”

”...”

”I have a small question?”

Gudako raised her hand.

”Why didn’t you just directly create land and oceans inside this universe? The Authority of Reason can do that, right?”

”Wasn’t shaping an entire planetary system kind of troublesome?”

Bonk—

Setsuna knocked her on the head.

”First, even though this miniature universe is small, its diameter is still two light-years. Fill two light-years of space entirely with land? The fact that you even dared think that means you need to retake astrophysics.”

”Second, this is for future expansion. When we enlarge the miniature universe later, I only need to fill it with more planetary systems—gradually expanding it to galactic scale, then to supercluster scale, and eventually to a true universe scale.”

”Hiss—”

”I was dumb—”

Gudako fled clutching her head.

”Then what about the people inside the miniature universe? I remember that if someone stays inside your hull and you retract the starship’s main body, the living beings inside get ejected, right?”

”Well, since the miniature universes exist in higher-dimensional space, retracting the Eternal Snowfall’s main body won’t affect the worlds inside.”

Observer glanced at the holographic interface.

”But the doors to the miniature universes will be folded back into the hull. If someone inside wants to come out, the Commander will have to deploy part of the rigging to release them.”

”...So this thing can double as a prison?!”

After finishing Universe No.1.

Setsuna took Tiamat and continued the great work of Genesis.

Shua—

Passing through the bridge and into the lower compartments.

They entered another void of chaotic darkness.

”This is Universe No.20—the largest miniature universe. Its radius is ten times that of the Solar System.”

”If the Commander wants to build megastructures inside the Eternal Snowfall, this universe couldn’t be more suitable.”

Observer gestured animatedly.

Beside her, Compiler continued tapping at an interface with the mechanical arms of her rigging.

”Constructing megastructures inside a small world bubble to supply one’s own energy... mm, this is a design unprecedented in history. Worth studying.”

”Hiss—”

Universe No.20 felt vastly larger than the previous one.

A miniature universe was essentially a spherical space. In three-dimensional terms, expanding the radius tenfold increased the usable volume far beyond just ten times.

Weng—

Setsuna once again performed the miracle of splitting heaven and earth.

A blazing star manifested within the newly born cosmos.

But this time, he did not immediately create planetary systems. Instead, he created star after star.

Boom!—

Not far ahead, a massive fireball suddenly ignited.

Brilliant light burst forth in the darkness. Solar wind carrying streams of particles rushed toward them.

”Stabilize.”

With a grasp of his hand, the raging fireball steadied and collapsed inward, compressing into a spherical form.

The star gradually stabilized.

With a wave of his hand, the surrounding space distorted slightly, dragging the star far into the distance.

Some were G-type stars like the Sun. Others were blue-white B-type stars. There were even O-type stars—massive and scorching.

Like multicolored fireballs, they were created before their eyes, then pushed by invisible forces into the distant void, becoming stars in the sky.

Within the void, interference was minimal. Both the Authority of Reason and Void could be exerted to their fullest extent.

”Ah...”

Everyone watched without blinking.

To shape stars by hand, then arrange them across the cosmos—this was a miracle equal to that of a Creator.

Before long.

The sky blazed with brilliant starlight.

Though its scale was far smaller than the universe outside, knowing that every star above had been shaped by Setsuna’s own hands made the spectacle even more overwhelming.

”So the stars here... were all personally created by the Commander?”

”Then isn’t he, in the truest sense, a Creator?”

Several shipgirls felt dazed.

”Hah—”

Setsuna exhaled, feeling somewhat drained.

”Commander?”

Formidable stepped forward to steady him.

”It’s fine. Creating this many large bodies in a short time, and moving them around—it’s a bit tiring.”

Setsuna waved it off.

Positioning stars was also a technical task. Their gravitational influences had to be considered.

A slight miscalculation could cause collisions—or even produce a chaotic three-body problem.

He gazed at the starry sky of Universe No.20 and called over Akashi and several Siren girls.

He pointed toward the nearest sun.

”Arrange for the Bulins and Angeloids to begin constructing megastructures.”

”Mm... considering the energy supply requirements of megastructures, start by building several Dyson Spheres. The Eternal Snowfall can draw energy directly from the miniature universe. Later, I’ll add additional stellar power sources as needed.”

”Whatever celestial bodies you need, I’ll shape them for you. Ordinary stars, planets, pulsars, black holes—anything at all.”

In the past, constructing Galactic Wonders required carefully selected sites. Within a miniature universe built entirely from scratch, they could shoot first and draw the target afterward.

Whatever construction conditions or environment the Engineering Division required, Setsuna could simply create it.

”Understood, meow!”

Akashi’s ears twitched as she manifested her claw-shaped ship and led a group of Bulins rushing forward.

”Back to work, nya! We’re going to turn the Eternal Snowfall into a mobile Galactic Wonder, nya!!!”

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