Crossover Shipgirls: Building a Dimensional Empire from Scratch

At dawn, as the DITF world’s Earth welcomed another sunrise, the 13th City—its urban core—was already in motion.

This place had once been the seat of humanity’s supreme administration and the Seven Sages, serving as the governing hub for both this metropolis and all other fortress cities.

Now, under the reconstruction efforts of the Angeloid and the Bulins, it had been transformed within days into a massive silver-gray administrative tower. The flag of the Starsea Empire fluttered proudly above it, and patrols of Angeloids filled the surrounding streets.

Inside the top-floor office of the administrative tower sat a woman in uniform, her hair tied neatly, her face flawless and serene.

Sophons.

Before her floated dozens of holographic interface windows—enough to make an ordinary person dizzy—but she handled each task in perfect order and precision.

This high-performance artificial intelligence had taken full charge of managing the Starsea Empire’s vassal worlds. Through the Sophon network, all reports from the vassal worlds could be instantly relayed to the main base and the Eternal Snowfall.

”Commander, this world differs somewhat from our previous vassal territories,” Sophon reported after conducting a comprehensive planetary scan.

”The Earth here has suffered severe environmental damage. Most mineral and petroleum resources have been nearly exhausted.”

”In addition, about 30% of the planet’s surface suffers from extreme desertification and radiation pollution.”

”The remaining human population is two hundred and thirteen million. Birth rates are extremely low, and the majority have undergone the immortality serum transformation, resulting in the complete loss of reproductive capability.”

She compiled all planetary data and transmitted it to the Eternal Snowfall.

”If we wish to raise this world’s productivity to match other vassal systems, substantial upfront investment will be required.”

In the DITF world, traditional nations had long ceased to exist. The United Human Government had collapsed amid endless civil wars and the protracted conflict with the Klaxosaurs.

Now, only isolated fortress cities remained, scattered across barren wastelands and loosely connected in a federal structure.

As for resources… if humanity here had enough to sustain itself, they never would have recklessly overexploited magma energy and triggered the chain of disasters that followed.

”Hm…”

Setsuna thought for a moment.

”Prioritize resource allocation to worlds with higher yield potential. We’ve got over a dozen vassal universes waiting for the Angeloids and Bulins to develop.”

”As for this one… we can give them a temporary tax exemption. Have the Angeloids lead the reconstruction efforts and rebuild civilization as quickly as possible.”

A barren world, no matter how much one scraped at its surface, wouldn’t yield much profit.

As a devout believer in sustainable exploitation, Setsuna decided it was best to implement sustainable development policies among his vassal worlds first.

”Oh, and since most of the humans here are immortal, that makes them ideal laborers, doesn’t it? They created this mess—so let them pay it back. Mobilize them all.”

”Yes, understood.”

Receiving Setsuna’s directive, Sophon swiftly initiated the next phase of operations.

Across every city, under the supervision of Angeloids, all available manpower was mobilized.

Although the population was low, the immortality serum had made the workforce ratio remarkably high.

”In the past, you indulged in your own desires, exploiting magma energy and destroying your environment. Even with the VIRM’s influence, you all benefited from it,” the Angeloids announced to the people.

”Now, it’s time to repay the debt you owe to your own world.”

The Angeloids distributed tools and began directing the population to reclaim the wastelands and expand the cities.

Meanwhile, adhering to the principle of ’not troubling the Commander,’ Sophon assigned a number of Angeloids to escort bewildered humans into outer space—to mine asteroids.

The collected resources were then smelted, refined, and funneled directly into planetary reconstruction.

After all, vassal worlds were not meant to drain their ruler’s resources.

If the Commander had to constantly demand tribute from his vassal worlds, it would be disgraceful—other Sophons might even mock her for it.

”???”

The humans never could have imagined that their first trip to space… would be to mine ore for their overlord.

Absolutely incredible.

”You’re a spacefaring civilization, right? Shouldn’t robots be way more efficient than us? Why make us do it?!”

At one of the asteroid mining stations, several humans voiced their existential frustration.

”We’re not your babysitters. If you thought joining the Starsea Empire meant you could live a life of luxury without lifting a finger, you were mistaken.”

”We’ll guide your civilization’s development and provide you with advanced technology—but that doesn’t mean you get to sit around doing nothing.”

The Angeloids’ response was cold and absolute.

Within the main base, Angeloids acted as obedient attendants, faithfully executing orders. But across the vassal worlds, alongside the Sophons, they were administrators.

”Move it!” one of them barked.

The Angeloids began drawing up meticulous work schedules.

”Hmm, since you’re all immortals now, that actually makes things easier. Let’s start small—say, mining on Mars for about… three thousand years.”

”Don’t worry, we’ll make sure your basic living conditions are guaranteed.”

”Wha—what?!”

...

Elsewhere, far from the cities, out in the wasteland—

Clang—

A small shuttle landed on the barren ground.

Setsuna stepped out alongside several shipgirls and the Klaxosaur Princess.

Before them lay a vast expanse of Klaxosaurs—countless in number, large and small, all sprawled across the plain.

They emitted deep, resonant hums, communicating with the Klaxosaur Princess.

It was everyone’s first time seeing the Klaxosaurs up close.

Their bodies were covered in rocky, unknown material, most of them dark blue in color. Sensors detected intense high-energy signatures emanating from them.

The Klaxosaurs were once Klaxosaurians like the Klaxosaur Princess herself—but in order to resist the VIRM, they had abandoned their consciousness and transformed into living weapons. Some had even sacrificed their combat ability to turn into magma energy, supporting their kin.

”It’s over. The VIRM have been destroyed,” the Klaxosaur Princess said softly.

The massive serpent-like Klaxosaur she once rode raised its head, gazing first at Setsuna, then at the shipgirls behind him.

Finally, it lowered its head gently before the Klaxosaur Princess.

”They’re the ones who helped us destroy our enemies. Your mission is over now,” she said, turning toward Setsuna to introduce him to the Klaxosaur horde.

”Can they understand you?” Gudako asked curiously.

”I don’t know,” the Klaxosaur Princess replied, shaking her head. ”But they are still my kin. Even if their minds are gone, they can still feel my emotions.”

Realizing that the great threat had finally been vanquished, the Klaxosaurs let out low, rumbling cries—mournful yet joyous.

”Thank you all… for enduring these tens of millions of years,” the Klaxosaur Princess whispered, gently stroking the serpent’s armored scales.

”Let the Klaxosaurs live here,” Setsuna said. ”This area will be designated as their sanctuary. No humans will disturb them.”

”Perhaps, someday, we’ll find a way to restore them to their original forms.”

He spoke with quiet respect. These beings had sacrificed their minds to defend their world—he owed them that much.

”...Thank you.”

The Klaxosaur Princess bowed slightly, her voice soft but sincere. Restoring the Klaxosaurs to their true selves was practically impossible—but if it was Setsuna, she found herself wanting to believe.

”Go now,” she said, patting the giant Klaxosaur’s neck.

”I’ll be leaving this world for a while. Behave yourselves—and don’t cause trouble for the Commander.”

ROAR—

The Klaxosaurs let out deep, resonant howls in farewell before slowly burrowing back underground, clouds of dust rising as they vanished beneath the surface.

”Goodbye~”

Everyone waved as they disappeared, filled with mixed emotions.

”Hm…”

Setsuna opened his holographic interface and checked over the mission data.

With that, the DITF world had been completely conquered.

This expedition’s haul: one ship full of lolis, one Klaxosaur Princess, several FRANXX mechs, and one discounted copy of the VIRM’s Human Instrumentality Project.

”A grand victory. Time to head home!”

...

A few days later, everything in the DITF world had finally settled into order.

It had always been a barren planet—no scenic beauty, no real treasures to explore.

Once all affairs were arranged, Setsuna led his fleet on the return voyage.

Whoosh—

Passing through the teleportation anchor, the familiar blue planet appeared before them.

The Eternal Snowfall remained parked in Earth’s orbit; after activating its anti-gravity system, it functioned as an artificial satellite of the planet.

The crew, meanwhile, boarded smaller starships to descend through the atmosphere.

Before long, the fleet broke through the clouds, and the capital came into view below.

”Commander! The Commander’s back again!!”

”Hmm, that was quick this time, wasn’t it?”

Every time the expeditionary fleet returned, it was met with cheers from those who had stayed behind in the capital.

Groups of little lolis, Spirits, and Heroic Spirits alike raced toward the starship landing base, eager to see what new companions—or curiosities—the Commander had brought back this time.

Click—

As the hatch opened, Setsuna was immediately tackled by Mio and Tohru.

”My dear husband, it’s been so long~!”

”I wasn’t gone that long, was I?”

Setsuna smiled, hugging Mio and planting a kiss on her cheek.

The Spirit of Origin was pure and beautiful, her figure flawless—holding her in his arms was simply irresistible.

”Hey, Master… how many girls did you pick up this time?”

”You haven’t spent time with me in ages. Tonight—you, me, no excuses.”

Jeanne Alter crossed her arms, face flushed but voice stern. She envied how freely Tohru and Mio expressed their affection, yet she couldn’t bring herself to be as open.

”Don’t be so tsundere. You and Jeanne d’Arc can come together.”

Setsuna ruffled her hair teasingly, then snapped his fingers.

”Alright, come on out—check out your new home.”

”...”

A group of little girls peeked nervously from the ship’s doorway.

They were just children—formerly confined in the ”birdcage” cities, isolated from the outside world. Apart from a few caretakers and fellow test pilots, they had never known freedom.

Now, after being suddenly whisked away on a starship and brought to a vast unfamiliar city, they were clearly overwhelmed.

”Go on,” Illustrious said gently, patting one of the girls on the back. ”Take a look around. This will be your home from now on.”

”It’s much nicer than where you used to live.”

So vast.

That was the first impression 02, Ichigo, and the others had upon seeing Constantinople.

No glass dome blocked the sky here—starships could fly straight into space.

The city’s scale dwarfed their former world; its architecture was grand and boundless. Shuttles and Angeloids glided between towers, giving life to a world both prosperous and magnificent.

For the first time, they felt a sense of true freedom.

They had stepped out of a cage—and into a vast open world.

”Yo, more kids? Commander, are you some kind of lolicon?” Jeanne Alter remarked dryly, watching Illustrious and Shoukaku lead the new arrivals out.

”They were treated as tools for piloting mechs back there. Of course I had to bring them home.”

Setsuna flicked her forehead.

Soon, everyone noticed that among the group of lolis, two girls stood out.

The Klaxosaur Princess—and 02.

02’s skin was pink, her eyes a vivid green, and a pair of horns grew from her head. Held by Shoukaku, she looked around wide-eyed and frightened.

”B-big… so big…”

Her words came haltingly; she had once been kept as an experiment by APE, barely even taught to speak.

Only through Shoukaku’s patient teaching could she now form simple sentences.

The Klaxosaur Princess, slightly older—a young maiden—had a single black horn, long silver hair flowing down her back, and faint bluish skin.

Stepping gracefully out of the ship, she gazed curiously at the assembled Spirits, Heroic Spirits, and lolis.

But what drew everyone’s attention most was her attire—or rather, her lack of it.

Only a few mysterious black ribbons covered her vital parts, leaving the rest of her stunning figure exposed.

And from her back extended eight jointed, limb-like tendrils, swaying gently in the air.

”This is the Klaxosaur Princess, leader of the Klaxosaurs—and the last of her kind. After the VIRM threat in the DITF world was eliminated, she wanted to come see this world.”

”The one beside her, 02… hmm, I suppose you could call her the Princess’s clone?” Setsuna explained.

”She’s nothing but a counterfeit,” the Klaxosaur Princess snorted, clearly unimpressed with 02.

After all, 02 had been created by Dr. FRANXX using the Klaxosaur Princess’s hair to forge a weapon against her people. Facing a clone made by her former enemies was naturally unpleasant—but since the VIRM were gone, she had no reason to argue with a child.

”Princess, huh…” Everyone looked at the Klaxosaur Princess with a mix of surprise and curiosity.

”I’ll have someone show you around the capital,” Setsuna said, patting her shoulder. ”We’ll arrange food, lodging, everything you need.”

”No need for that. I’ll live underground.” The Klaxosaur Princess shook her head firmly.

”???”

”Come on, we’re an interstellar civilization now! You still want to hide underground like before?!” Yat Sen said with a half-helpless, half-amused sigh.

Two Angeloids were soon assigned to guide the Klaxosaur Princess through the city.

”As for the lolis, send them to school,” Setsuna continued. ”Help them adapt to the new environment. Chen Hai, get their enrollment handled.”

”Understood~”

A glamorous shipgirl in a short cheongsam and black stockings nodded, stepping forward to lead the group.

”Oh, and by the way,” Setsuna added. ”They were originally trained as FRANXX pilots—basically Gundam prodigies. Aside from regular academics, let’s continue their mecha training. We’ll modernize and convert the FRANXX units into single-pilot frames.”

He thought for a moment, deciding to make full use of their talents.

”Oho, special talent students?” Chen Hai smiled knowingly. ”Little lolis piloting Gundams… feels a bit weird, doesn’t it?”

...

Later that evening, in the Research Division—

Setsuna stood before a group of excited research lolis and Siren engineers, showing them the spoils of his expedition.

”Here—several FRANXX units, including the Strelizia, Delphinium, Argentea, and Genista. Their blueprints are also here, along with some of Dr. FRANXX’s unfinished concepts. Try implementing them.”

He set a line of mechs and a pile of data disks in front of the group.

”Rework the FRANXX frames. They’re essentially biomechanical mechs, structurally different from Gundams. Replace their outdated systems with our propulsion thrusters, corrosion missiles, and arc cannons—then adapt them for single-pilot operation.”

In the DITF world, FRANXX units had required dual pilots for two main reasons: first, the immortality serum had altered human physiology, making them incompatible with Klaxosaur-based mechs; second, the pilots themselves were ordinary humans without special abilities—their individual mental strength was too weak to synchronize with a FRANXX.

The Starsea Empire, however, possessed advanced genetic evolution, Spiritization, and MANTIS-level bio-augmentations. Even a common soldier’s strength was beyond superhuman—so dual-pilot limitations were irrelevant.

”Ohhh…”

The research lolis and Siren engineers stared in fascination, Daedalus gazing long at the Strelizia with awe.

These mechs were unlike any Gundams they’d seen before—their designs carried a strange, organic beauty.

”Oh, right,” Setsuna added casually. ”I also brought back some VIRM data—they were working on something like the Human Instrumentality Project.”

”And a few samples of magma-energy extract. The humans there used it as an immortality serum—it grants eternal life, but at the cost of reproductive ability.”

He handed over a small pile of items to Akashi.

”We don’t have any immediate use for them, so just catalog and store them for now.”

”Got it, nya~!”

The cat-eared engineer cheerfully hugged the items to her chest. Even if they weren’t useful, she loved hoarding things like a hamster.

”Commander, Akashi loves you the most, nya!!!”

The catgirl pounced on Setsuna, rubbing her head affectionately against his chest.

”???”

”Do you love me, or just the things I bring you?”

”Both, nya~~~!”

—

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