Crossover Shipgirls: Building a Dimensional Empire from Scratch

City 6 Fortress.

Located far from the starship landing zones, this city had not yet been struck by the Angeloid forces. While neighboring cities burned in chaos, City 6 remained oblivious to the unfolding disaster—its communications completely severed. All they knew was that one city after another had gone silent.

Among them was City 13, home to Strelizia and Dr. FRANXX—the most critical human stronghold and the heart of humanity’s war against the klaxosaurs.

”City 13—no response. Confirmed: City 13 is lost.”

”Cities 5, 11, and 15—APE Command calling! Please respond, repeat, please respond…”

Inside the city’s futuristic central administrative complex, the officials’ voices were tight with anxiety as they desperately attempted to make contact.

Zzz—Zzz—

Only static answered them.

Under Nymph’s powerful electromagnetic interference, all electronic communications across the planet had been rendered useless—no internet, no radio, no telegraph.

”No response, sir,” a uniformed officer reported to the seven figures seated high above.

Each wore identical white robes trimmed with gold, and masks that hid their faces completely. They varied in height and build, their collective presence mysterious and imposing.

The Seven Sages of the APE Council.

They were the supreme commanders of humanity’s ruling body, APE—leaders of every fortress city and overseers of all FRANXX operations.

The children knew them by another name—”Papa.”

No one had ever seen the faces beneath their masks. It was said they had ruled humanity since ancient times, orchestrating every major initiative—from the war against the klaxosaurs to the development of magma energy.

”City 13 has gone dark? Dr. FRANXX is stationed there, along with…”

”The children—what about them?”

The tallest and most elaborately dressed of the seven asked.

”Apologies! No transmissions have come through! City 13 isn’t responding at all!” the officer stammered.

”It appears the entire planet is under severe electronic disruption!”

”...”

The Seven Sages exchanged glances, as if silently communicating through their masks.

They didn’t dwell long on the cause. Their leader issued a crisp command.

”...Send a team.”

”Strelizia and the experimental subject must not be lost.”

”Yes, sir.”

Ten minutes later—

Outside the city, a sizable FRANXX squadron was assembled.

Pilots climbed into their mass-production models, while accompanying ”adults” manned support vehicles beside them.

”We’re heading to City 13. It may have been attacked by klaxosaurs—we’ve lost contact.”

The commander briefed them with a grim expression.

”Lost contact?”

The pilots exchanged uneasy looks.

A klaxosaur assault powerful enough to destroy a city without even a distress signal… that was beyond anything they could imagine.

Still, it was also the perfect chance to prove themselves.

”Alright—Team One and Team Two, split up and move out.”

”Prepare to—”

BOOM—

The ground suddenly trembled.

”?”

”An earthquake?”

The pilots froze.

The tremors grew stronger by the second.

It felt as if something vast was stirring beneath the earth.

”Klaxosaurs!! Klaxosaurs incoming!!!”

The alarm blared from the city walls.

Dozens of kilometers outside the city, the ground erupted—tens of thousands of klaxosaurs bursting forth from below.

Most were blue-black in color, their bodies made of segmented carapace-like material.

The smaller ones—resembling spiders, insects, and other small beasts—scurried ahead as vanguards.

Behind them came the massive ones, several times larger than FRANXX mechs, their forms warped and monstrous.

”Klaxosaurs attacking!!!”

”...”

The newly assembled FRANXX battalion froze for an instant, stunned by the overwhelming sight before them.

They thought they were dreaming—none of them had ever seen such a massive klaxosaur assault.

”Defend!!!”

Boom boom boom—

Cannons along the city walls roared to life, shaking the soldiers out of their shock. They scrambled to their mechs, taking up arms to hold the line.

Slash—

Boom!!!

The battle erupted in full.

On the battlefield, klaxosaurs were torn apart one after another by FRANXX units and artillery fire. Blue blood sprayed through the air, raining down like a macabre storm.

But the defenders were falling too—many FRANXX mechs were smashed aside or destroyed outright, their remains scattered along the walls.

”There’s too many! The mass-produced FRANXX can’t hold them off!!”

The commander watched in horror as their steel defensive line was pushed back inch by inch.

”Why… why are the klaxosaurs here?!”

”Could it be… they’re coming for APE?!”

At the thought of the Seven Sages within the city, cold sweat ran down his neck.

”Prepare to evacuate!!”

Suddenly—

Whoosh—

A sharp sound split the sky.

The Angeloid vanguard had arrived.

Hovering high above, they surveyed the chaotic battlefield below—humans and klaxosaurs locked in desperate combat.

”Reporting to Master. Confirmed: the Seven Sages, humanity’s top rulers, and the Klaxosaur Princess are both present.”

Ikaros’ report came through clearly as she scanned the area.

”Angels?”

The human defenders looked up in disbelief.

White wings, radiant figures—they thought they were hallucinating. Angels, descending onto a battlefield?

Before they could process what they were seeing, the sky grew darker.

Descending behind the Angeloids came the vast shadow of the orbital fleet—massive starships, each stretching for tens of kilometers.

Even without the Eternal Snowfall herself present, the combined fleet of shipgirls blotted out the sun.

A colossal shadow blanketed the battlefield and the entire city.

”Ah…”

Civilians instinctively looked up, swallowing hard.

Even the klaxosaurs and FRANXX pilots halted mid-battle, staring skyward, weapons lowering unconsciously.

”What is that…”

With humanity’s current level of technology, none could comprehend what they were witnessing.

”Are they from another city?”

”Reinforcements?”

”No, wait—what’s with that emblem? I don’t recognize any APE division using that insignia…”

”And those angels—where did they come from? Are gods real after all?!”

Whispers spread through the city like wildfire.

The klaxosaurs, however, reacted far more aggressively. As if provoked, they immediately regrouped into defensive formations.

Those with ranged abilities raised their weapons, aiming toward the sky.

”Easy. We’re not VIRM—I have no hostility toward you.”

Setsuna’s calm voice echoed from the flagship, transmitted directly across the battlefield.

”What?”

The humans stared up, bewildered.

They soon realized that Setsuna wasn’t addressing them—but the klaxosaurs.

Could the klaxosaurs understand human speech? And what was a ”VIRM”? No one understood.

Then—

BOOM!

From the midst of the klaxosaur swarm, a gigantic serpentine creature—nearly a hundred meters long—emerged from the ground, its scales glistening dark blue.

It coiled upward, raising its massive body, and opened its jaws toward the starships above.

Standing within its maw was a girl.

Her skin was pale cyan, her long pink hair cascading down to her feet, and a black, horn-like crown rested atop her head. Her green eyes glowed faintly beneath the shadow of the serpent’s mouth.

She wore a strange, silky fabric that concealed her form, and from her back extended eight black, segmented appendages—like insect limbs, eerily similar to Observer’s rigging.

Facing away from the city, the people below thought the klaxosaur was preparing to attack the fleet.

”You… you’re not human. But you’re not VIRM either. Who are you?”

The girl’s wary voice echoed upward as she gazed at the fleet.

”Yo, Klaxosaur Princess—nice to meet you.”

Setsuna raised a hand in greeting, smiling faintly.

”Ahem, simply put, we’re humans from another world—here to conquer this one.”

”Ever flown on a starship? No? How about coming aboard? I’ll take you to smash your old enemies.”

...

”What an entrance…”

Gudako and the shipgirls stared down at the scene below—where the Klaxosaur Princess sat upon the open jaws of a colossal serpent-shaped klaxosaur.

The girl, who appeared barely older than Gudako herself, commanded the entire klaxosaur horde from her throne of scales.

”So young… guess princesses are always cute girls, huh?”

The Human Evil leaned forward curiously.

”Uh, her actual age is around sixty million years. She’s from a previous civilization of Earth,” Setsuna corrected casually.

”???”

”A sixty-million-year-old girl?!”

Gudako nearly jumped.

”I thought a few-thousand-year-old dragon girls, fifty-millennia immortal, and little Griseo were already unbeatable—what kind of ancient relic is this?!”

”Forget it. Let’s just call her immortal. Honestly, if you didn’t say sixty million, I’d think she was sixteen.”

”...”

The Klaxosaur Princess paid no mind to the chatter on the bridge. Her emerald eyes locked with Setsuna’s across the vast distance, meeting his calm gaze through the starship’s viewport.

”You… come from somewhere farther away?”

Her voice was ethereal, and her eyes flickered as she studied the flagship and its accompanying vessels.

Indeed, their design was nothing like the VIRM ships she remembered.

Even stranger—the people aboard were human. That alone made her curious.

”Yes, though explaining another universe is a bit complicated. Why not come aboard? We can talk properly,” Setsuna offered, his tone smooth and disarming.

”...”

The Princess remained seated upon her klaxosaur’s head, silent for a moment. She tilted her head slightly, closing her eyes as if deep in thought.

”The other cities… all that destruction—was it your doing?”

”Of course. This world will soon be integrated into the Starsea Empire. From now on, it will fall under my unified administration.”

Setsuna smiled faintly.

”But don’t worry—we’re not like the VIRM. No assimilation, no annihilation. The planet’s people can continue as they are.”

”Oh, and the war between humans and klaxosaurs? That ends today. Under imperial rule, humanity and klaxosaurs will coexist in harmony.”

In ancient times, the klaxosaurs had been Earth’s original inhabitants, building a civilization far greater than humanity’s.

When the alien VIRM invaded, the klaxosaur race fought to the brink of extinction to defend the planet.

To prevent another invasion, they retreated underground—some transforming into magma energy, others evolving into the living weapons now known as klaxosaurs.

Unknowingly, tens of millions of years later, humanity arose—and became their unwitting enemies.

Driven by the pursuit of the immortality serum, humans mined magma energy recklessly, provoking the klaxosaurs and perpetuating their endless war.

”...”

The Klaxosaur Princess raised her hand, and the restless klaxosaurs below fell silent, withdrawing their weapons aimed at the fleet.

She closed her eyes again, clearly pondering Setsuna’s proposal.

There were far too many inconsistencies—his presence, his fleet, his perfect knowledge of their buried history.

No one on Earth should know of the klaxosaur race’s true origins—not even the humans’ so-called leaders.

Unless… he was a VIRM himself. But that couldn’t be—VIRM had no human forms.

”...Very well.”

After a long pause, the Princess finally spoke.

”But before that, there’s one thing I must deal with first.”

She turned her gaze toward the direction of the administrative capital.

”Oh, the Seven Sages? Ikaros—go fetch them.”

Setsuna wasn’t surprised in the slightest. He waved his hand calmly.

The highest authority of human civilization, APE, was nothing more than a puppet regime controlled by seven VIRM-created commanders—the so-called ”Seven Sages.”

Naturally, they too had to be purged.

”Considering their non-biological composition… Nymph, you’re going too.”

The blue-haired loli angel nodded.

With a flutter of wings, she leapt from the bridge, following Ikaros down toward the city below.

”You… even know about them? Why capture the Seven Sages?”

The Klaxosaur Princess blinked, genuinely surprised that Setsuna had stolen the words right out of her mouth.

”First, to lock them in a lab for study. Our science division is quite interested in researching alien life forms.”

”Second, we’re going to trace their signal back to the VIRM homeworld… and deliver them a little warmth.”

Setsuna grinned, opening the starship’s hangar bay and releasing a small shuttle.

”Come on, be good. Hop aboard—I’ve got something nice waiting for you on my ship.”

...

Meanwhile—

As the klaxosaur horde suddenly halted their advance, the battlefield fell into an eerie silence.

Three forces now faced each other outside City 6.

On the ground stood the klaxosaur army and the FRANXX units defending the human fortress.

In the sky hovered the Starsea Empire’s fleet—its formation gleaming under the clouds, flanked by squadrons of Angeloids patrolling the air.

When the klaxosaurs stopped attacking, the FRANXX units dared not make a move. They were too far from the front lines to understand what had just happened, completely unaware that the Klaxosaur Princess was in contact with Setsuna.

They only knew the battle had suddenly stopped.

The unexpected ceasefire gave the exhausted defenders a brief moment to breathe—but the looming starships and radiant Angeloids above filled them with suffocating dread.

”...Hah...”

The city’s defense commander stared nervously at both the klaxosaurs and the fleet above.

He could only hope they’d turn on each other—best case, both sides would tear each other apart, sparing his troops from the slaughter.

”Can we contact the other cities? Anyone seen these ships before?” he asked.

”No, sir.”

His officers shook their heads rapidly.

”All fortress cities have lost communication—total blackout.”

”...”

”Forget it, then. Pull the FRANXX units back.”

The commander thought for a moment before issuing orders.

”And the garrison troops—return inside the city walls. Don’t provoke the klaxosaurs.”

”If those beasts start fighting the ships in the sky, we don’t want to be caught in the crossfire.”

He had no desire to throw his men into a fight against the overwhelming swarm outside.

From the defenders’ point of view, the klaxosaurs seemed to be facing off against the alien fleet. The smartest move was to retreat and survive.

Clack—clack—clack—

The FRANXX units carefully withdrew from the outskirts, retreating behind the walls.

The city gates shut tight, and the team leaders gestured for silence, fearing even the slightest noise might trigger another attack.

The garrison troops manned the ramparts, setting up heavy weapons just in case.

”First Battalion—secure the east side.”

”Second Battalion—guard the main gate.”

”Send a recon squad—light gear only. Head out and try to reach any nearby cities.”

The commander continued giving rapid orders.

”With the entire klaxosaur army gathered here, the outer routes should be clear. Find out what’s happening elsewhere.”

”Understood.”

A small scout team quickly packed their gear and slipped out through a hidden passage.

”Phew—”

The commander exhaled in relief.

But before he could relax, a messenger sprinted up and saluted.

”General! Orders from the High Council—we’re to capture that enormous klaxosaur at any cost!”

He pointed toward the massive serpent-like creature towering in the distance.

”Their exact words, sir: that klaxosaur is critical to ending the war. Capture it, no matter the cost.”

”What?!”

”They’ve lost their minds!”

The commander stared in disbelief at the enormous creature surrounded by its kin.

Even at a distance, it was clearly much larger than any other klaxosaur—likely the leader itself. But even with binoculars, its full form was obscured.

Charging into that swarm to capture it would be suicide.

”High command insists, sir! Capturing that klaxosaur will end the war!”

The messenger faithfully relayed the Seven Sages’ command.

For every city, APE’s orders were absolute—beyond question.

”...”

”This… this is madness…”

”If we attack head-on, the FRANXX units won’t stand a chance. And those ships in the sky…”

The commander rubbed his temples in frustration.

”Maybe we could send a small team as bait? No… if the klaxosaurs ignore it, it’s pointless.”

”And even if we somehow reached that giant serpent, how many FRANXX would it take to capture it? A hundred? Three hundred? More…”

His mind raced in circles.

Then—

Whoosh—

Above the city, the Angeloids suddenly moved.

They swooped down from low altitude, wings cutting through the air, heading straight toward the APE central command tower.

At the same time, several klaxosaurs stirred, moving to encircle the same area.

”???”

Fwoosh—

The commander’s eyes widened as incoming corrosion missiles streaked toward him, rapidly expanding in his view.

”Damn it—don’t tell me they’re working together?!”

—

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