Crossover Shipgirls: Building a Dimensional Empire from Scratch

[Flight path confirmed.]

[Starship entering sublight cruise mode.]

After taking the newly arrived Arbiters for a stroll around the capital and treating them to a grand ”Staring at the Stars” feast, at the Arbiters’ strong insistence, everyone boarded Observer’s vessel to meet the Commander.

Shuaa—

The anti-gravity ship accelerated swiftly, breaking through the atmosphere in an instant.

Outside the porthole, the view switched in the blink of an eye to a boundless sea of stars.

”Whoa...”

The Arbiters once again felt a wave of dizziness.

The sight of space was utterly foreign to them.

Even though the Arbiters possessed high levels of military and spatial technology, due to certain constraints, they had never managed to build a true interstellar vessel.

They had never set foot among the stars.

The Starsea Empire’s solar system was unimaginably prosperous. Beyond Earth’s orbit, countless fleets of starships could be seen at any moment.

They traveled constantly between star systems, forming a bustling network of traffic routes.

Mining stations and research bases filled every planetary surface—there was none of the cold emptiness one might imagine of the cosmos.

”You... have cities on the moon?”

Empress was astonished to see the moon’s surface covered with vast clusters of buildings.

On an astronomical scale, even to the naked eye, this moon was nothing like the barren, desolate rock she had known.

The cities sprawled across the surface were second only to the capital she had just seen. Rivers and seas could even be spotted glimmering faintly across the lunar plains.

The broad swath of deep blue across the western hemisphere was especially striking.

”Didn’t I just tell you? The moon is the Starsea Empire’s scientific hub—home to the Departments of Engineering, Physics, and Life Sciences.”

Observer explained in a tone one would use for teaching primitives.

She pointed toward the porthole below.

”The lunar seas were made by Aqua. The Research Department said they could use her powers to establish a water cycle system there.”

”Look, that blue-haired goddess down there shopping—that’s her.”

At the lunar base, Aqua was being fawned over endlessly by the research lolis—”Lady Aqua this,” ”Goddess that”—so delighted that she practically lived in the labs, helping with experiments day and night.

”A goddess... from Heaven?”

Empress, Lovers, and the others felt confused. That airheaded girl looked nothing like the image of a divine being in their minds.

”Yeah, but the Research Department’s busy studying the wonders lately, so let’s not bother them.”

The ship continued its course toward the Starbase.

Along the way, Observer proudly introduced one after another of the Starsea Empire’s achievements, leaving the Arbiters entranced.

”That’s the Mars Smelting Base. In the later stages of planning, we intend to make Mars the resource-processing center of the Solar System.”

”All metals, ores, and primary resources are processed there into alloys and refined materials, then distributed across the system.”

”Whoa...”

Mars had taken on a silvery-gray hue. Upon closer look, that was the color of the endless factories covering its surface.

The soil was completely overlaid by massive processing plants stretching from equator to pole, where countless Angeloids and Bulins worked busily.

”Those installations in Jupiter’s orbit—that’s the Sentry Array base, one of the first Galactic Wonders we are constructing...”

”And there, that’s the Venus Outpost—we’re in the middle of terraforming that planet...”

”Whoa...”

The twelve Arbiters were left utterly shaken.

Compared to the awe inspired by the capital, what they saw in space was even more overwhelming.

All their pride and sense of superiority evaporated instantly.

Not only the Arbiters—if the entire Siren Legion stood before the Starsea Empire now, they too would appear utterly insignificant.

When they saw the galactic chart displaying the Empire’s borders spanning thousands of light-years, the Arbiters finally understood the true scale of this interstellar giant.

”Some of our data should probably be archived now.”

Temperance quietly operated her ship’s holographic console.

Before departing, they had prepared some technologies to share with the Experimentals and the shipgirls—hoping to help them build their new home.

Now it seemed that most of the technology they had brought was already outdated in the Starsea Empire.

”Ah, your ship looks quite advanced too—”

Still shaken by everything, Empress, Lovers, and several other Arbiters turned their attention to Observer’s vessel.

After all, they were all Sirens—once familiar with each other’s capabilities.

But this new, starship-form Siren vessel was something entirely different.

Its internal structure still retained the Siren aesthetic, but not a single piece of its equipment or weaponry was recognizable to them.

”Oh? Your fire-control system’s been completely reworked? And what’s this armament...?”

Empress peered curiously at Observer’s main control console, glancing left and right, occasionally touching the holographic interface to examine the data.

”Pretty cool, huh?”

”Ever played with one of these before? Bet you haven’t!”

The little loli puffed up with pride, waving her tentacles triumphantly.

”This is a genuine faster-than-light starship! It can jump—yes, jump! Do you even get what that means?!”

”See those emitters along the port and starboard sides? Those are photoid cannons! One of them could shatter a sun! If you want to broaden your horizons, I’ll take you to the Three-Body universe later!”

”Anyway, can’t just go blowing up this star—we’re saving it for future development.”

”...”

”Shatter... a sun?”

The Arbiters began to develop a new understanding of the Experimentals’ destructive capabilities.

”I say, why don’t you let us join the Experimentals instead? Or at least bump up their rank within the Siren hierarchy...”

Observer sidled up to Dreamweaver and whispered conspiratorially.

”After all, we’re clearly the strongest division now...”

”...”

Dreamweaver didn’t reply, only casting a mildly astonished look her way.

”Your self-awareness has grown... stronger.”

The surrounding Arbiters were stunned.

”Wait—you’re seriously thinking of rebelling?!”

”Whoever’s strongest commands the Arbiters! If you disagree, we can take this outside!”

Observer found it deeply amusing to bully her former superiors.

There was something immensely satisfying about turning the tables.

”...”

Compiler floated nearby, expressionless as ever, watching the loli and the Arbiters bicker.

After a moment, she spoke in her usual emotionless tone:

”Observer, have you ever considered something?”

”What?”

”When the Arbiters join the Starsea Empire, the Commander will likely refit them for interstellar operations as well.”

”So... isn’t it unwise to bully them now?”

”Eh?”

Observer froze.

”Oh... right... uh...”

”Can we pretend that didn’t happen just now...?”

...

Amid the chatter, the ship arrived at the Solar Starbase.

At a stable synchronous orbit some distance from the star, the Eternal Snowfall stood tall and majestic in the void.

”So big...”

The Arbiters gazed upward in awe. From the capital to space, and now to a Juggernaut-class starship, the Starsea Empire’s splendor had surpassed every previous impression.

Before the planetary-scale warship, most of the Sirens were struck dumb with shock, following the Angeloids mechanically as they disembarked.

”When meeting the Commander, please maintain proper decorum. You have been granted permission to receive a personal audience with Master.”

Icarus led the group through the ship’s corridors, drawing curious glances from the Arbiters.

Click—

As they passed through the long corridor, they marveled at the intricate structure within the starship.

Finally, at the uppermost bridge, they saw him—the leader whose presence had once existed only in the database, the figure who had reshaped the entire Azure world.

”Welcome. A pleasure to meet you.”

Setsuna sat in the command chair, before him a holographic table displaying billions of data streams.

Behind him shimmered the vast, radiant starfield.

On either side stood shipgirls, Spirits, dragon girls, and others—all watching the newcomers with mild curiosity.

”So strong...”

With just one glance, Empress could tell that none of these beings were ordinary.

Setsuna carried the same kind of power as the shipgirls—but magnified a thousandfold in sheer presence.

The dragon girls and Spirits were unfamiliar to them, but it was obvious: anyone who stood at the Commander’s side was no mere mortal.

”Commander~ I brought them!”

Observer leapt into his arms, tilting her head up expectantly.

”I showed them around the capital, took them to the moon and Mars bases, and gave them an overview of the Starsea Empire~!”

”So tired~ Commander, give me a massage!”

The Arbiters stared, dumbfounded at the sight.

They could scarcely believe that the same mischievous, sharp-tongued brat from before was now acting like a spoiled child in the Commander’s arms.

What in the world had turned her into this? Was it... the Commander?!

”Ahem—”

Setsuna patted the little loli’s head and set her down gently.

”Welcome, everyone.”

”As you can see, I am the Commander and leader of the Starsea Empire.”

”...”

At the back of the group, Dreamweaver floated forward silently.

”...I know.”

”Commander, we’ve met before.”

”You’ve met me before? When?!”

Setsuna was a little surprised—he didn’t recall ever having interacted with the Arbiters.

”Navigator... TB, she’s part of the Siren main system.”

Dreamweaver replied softly.

”From the moment you created her, I became aware of your existence.”

”Oh, that little one.”

Setsuna and the shipgirls remembered.

A few years back, after bringing Grey back, the nanobot collective and the Sirens had held deep exchanges in artificial intelligence research.

Together, using data left behind by Compiler, they managed to create a little loli AI.

Her full designation was the Sirens’ newest auxiliary intelligence personality—built to assist fleets with data management and tactical analysis.

Since the Starsea Empire’s shipgirls didn’t need an AI loli to join battles, she had simply been attending classes with the smaller shipgirls instead.

”Navigator... she’s yours now. Treat her well.”

Dreamweaver’s voice remained ethereal, just as before.

”Don’t worry—she’s doing great. Morning classes for general education, afternoon classes for interstellar warfare theory, and practical lessons on weekends. She even visits the Three-Body universe to study how to use colossus-class weapons.”

”It won’t be long before she becomes an outstanding war cri—uh, I mean, navigator, just like the Commander.”

Grey patted her chest confidently.

”...What?...”

Dreamweaver tilted her head, utterly confused, staring at the nanobot girl for a long time.

”...”

Setsuna gestured for the Arbiters to sit down, exchanging a few polite words.

Having witnessed the Starsea Empire’s splendor and technological might along the way, many of the Arbiters were still mentally overloaded.

All the arrogance they’d carried upon arrival had completely evaporated.

Now they huddled quietly around Dreamweaver, glancing about the starship’s interior with a mix of awe and guarded curiosity.

They were newcomers in every sense—and still a little wary.

”Why did you all lose contact for so long? And tell me about your situation before I arrived.”

Setsuna asked, genuinely curious about the Arbiters’ origins.

”...”

The Arbiters hesitated for a moment, but since the entire Siren Legion had reunited under the Starsea Empire, there was little point in hiding anything.

Empress spoke first:

”The world where the port is located was originally one of our experimental fields, designated as...”

”The Experimentals were conducting observational research on the shipgirls there. Under normal circumstances, once the observation period ended, we would have reclaimed that universe.”

As Setsuna suspected, the Arbiters possessed extremely advanced spatial technology—capable of traversing between parallel worlds within the same universe, observing, creating, and reclaiming multiple experimental universes.

”So basically, Purifier and Observer were toying with us all that time? I knew they didn’t seem that weak...”

Richelieu cast a sideways glance at the Siren girls.

”...”

”Later, when you pierced through space and arrived in the experimental field, I noticed you. You were an anomaly—an unknown factor that broke the field’s isolation and introduced unpredictable variables.”

”I attempted to restore and reclaim the field, as well as analyze your existence, but failed. The experimental field couldn’t be recovered through normal technological means. The resulting backlash caused a chain collapse of several parallel universes.”

Temperance, seated within her jellyfish-like rigging, continued the explanation.

”The Siren Legion wasn’t prepared for that. Many Arbiters were scattered across unknown space. It took a very long time to regroup the Arbiter Organization.”

”As for the Experimentals... within the void, we were unable to locate their coordinates. Only when the main system received Observer’s transmission did we confirm their location.”

”...Nice going.”

Gudako nudged Setsuna playfully.

”My fault? I practically entered the port zone naked back then.”

Setsuna shrugged.

He had used his system authority to tear through space and arrive in another world—if Temperance’s reclamation caused a glitch, that made perfect sense.

Still, regardless of how it happened, both the shipgirls and the Siren fleets had now gathered together—and that was what truly mattered.

As for the finer details of the Azure world, Dreamweaver could brief him later.

”In any case, from the looks of things, you currently have nowhere else to go, correct?”

Setsuna cleared his throat and looked toward Dreamweaver.

”As per standard procedure, if you’re willing to accept command, I can offer you protection within the Starsea Empire—and help you rebuild the Siren Fleet.”

”The capital’s Siren naval port is enormous. Normally, only five of the Experimentals are stationed there. You can easily move in without issue.”

”Additionally, all Arbiters are eligible for starship refits. Your base hulls seem sturdier than Purifier’s or Observer’s... hmm... pairing that with photon lances and photoid cannons wouldn’t be bad.”

”In time, you can form your own fleet and accompany me on interdimensional expeditions.”

The Experimentals, limited in number and function, didn’t possess strong combat capacity.

If the entire Arbiter Organization underwent starship-grade refits and formed a new fleet of Arbiters and Executors, their strength would be formidable beyond doubt.

”Hmm—”

Several Arbiters exchanged looks, minds already spinning.

On the way here, they had witnessed firsthand the combined might of the starship-class shipgirls and the Sirens.

Once, the Arbiter Organization had been the militant arm of the Siren Legion. But now... even a starship-converted destroyer might outmatch them.

The realization stung deeply.

Setsuna’s proposal was dangerously tempting.

As for accepting his command? Judging by how the Experimentals behaved, it didn’t seem like an issue at all.

”I agree!”

Empress nodded reflexively, then quickly caught herself, covering her mouth before glancing toward Dreamweaver.

”Uh... Zero, what do you think?”

”...”

Setsuna couldn’t help but think Dreamweaver resembled an offline AI mainframe. Whether she spoke or acted, her expression never changed—her face remained emotionless, unreadable.

Yet, undeniably, she was the very core of the entire Siren Legion.

”That is acceptable. For now, let us rest here, Commander.”

Dreamweaver’s voice was soft but clear.

”Good.”

Setsuna tapped the table lightly.

”Yat Sen, assign a group of Bulins to clear out a shipyard at the Starbase. Begin retrofitting the Arbiters’ Siren vessels.”

”As for the modification plans... discuss them with Compiler. She usually handles Siren refits.”

”Right, and you, Dreamweaver—what kind of refit do you want?”

He looked at the pale-skinned little loli.

”...”

”I don’t need one.”

Dreamweaver shook her head slightly.

”I wish to learn more about this place... and about all of you.”

”...What a strange Siren.”

The shipgirls exchanged glances.

The lower-tier Siren mass-production units had no self-awareness or emotion, and even as the Siren core, Dreamweaver seemed equally detached.

No one could tell what she was thinking.

”Alright then, go visit the Research Department later. If there’s anything you don’t understand, have the research lolis or Grey explain it to you.”

After thinking for a moment, Setsuna decided that cross-exchange between them couldn’t hurt.

...

A shuttle soon carried Dreamweaver and the Arbiters to the Starbase.

This facility was also one of the Empire’s key research hubs. Grey and the Angeloids led them on a tour across various departments.

”This is the Department of Life Sciences. The Starbase mainly focuses on genetic technology and theoretical biology.”

”In simple terms—genetic ascension procedures, meta-morph surgery, and space crop optimization. Though, shipgirls don’t really need most of that...”

”If you’d like to see Honkai Beasts and Danger Species, we can visit the lunar station later...”

”This area belongs to the Department of Physics, responsible for cutting-edge imperial technologies—hyperspace engineering, dimensional mechanics, and the like...”

”...”

Dreamweaver and the Arbiters listened quietly, occasionally asking peculiar questions.

Their scientific foundations differed considerably—and since the Starsea Empire’s science integrated technologies from countless worlds, some of it was simply beyond their comprehension for now.

”Magic Academy?! Magic??! You’re serious?!”

When they heard that the Empire even had mages, the Arbiters were utterly stunned.

While the scientific side of things was still within reach—something they could eventually understand through effort—the magical side was a total black box to them. Who could possibly explain what the Spirits, dragon girls, elves, and that group of goddesses even were?

”...”

After another round through the Engineering Department, the Arbiters took a closer look at the technologies behind starship conversion, marveling at the breakthroughs in faster-than-light travel and hyperspace jumps.

Several of them could barely contain their excitement—itching to get their own conversions started as soon as possible.

For shipgirls, the call of the sea was engraved into their very being.

—And the starsea... was a sea all the same!

”Commander, your civilization’s level of development has far surpassed our expectations.”

Temperance bowed slightly toward Setsuna.

”Before we departed, we extracted some data from our archives—intending to help the Experimentals and shipgirls evolve and develop further.”

”But now, it seems most of it won’t be necessary.”

”Oh? You were planning to support the natives?”

Setsuna chuckled.

”You’re a bit late for that. If you’d shown up a few years ago, back when we were still poor and empty-handed, I would’ve gladly taken all the help I could get.”

”Hmm... in most fields, your people have already surpassed us.”

Temperance replied honestly.

”However, in the area of Wisdom Cube research, we can still share some of our findings—as a token of gratitude for receiving us.”

”I believe you’ll find them quite valuable.”

”Oh? Planning to make more little shipgirls? Or maybe little Sirens this time?”

Gudako popped her head in eagerly.

”No. From other lost universes and experimental fields, we’ve discovered a different evolution pathway for shipgirls and Wisdom Cubes.”

Temperance shook her head.

”Commander, you must already know this—complete self-unshackling, evolving along a divergent path... the META form.”

—

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