Crossover Shipgirls: Building a Dimensional Empire from Scratch

Far out in the deep seas, over a thousand nautical miles from the port.

A small girl with white hair and yellow eyes sat atop a massive rigging.

In stark contrast to her petite figure, her rigging was enormous, flanked by eight colossal cannons, each over ten meters long. The rigging was surrounded by tentacle-like structures, resembling the sea creatures from which Sirens seemed to draw inspiration.

This was the Observer, another high-ranking Siren from the Terminal Unit, much like the Purifier, tasked with overseeing this section of the seas.

Her delicate feet splashed idly at the water's surface as she lay sprawled out, gazing absentmindedly at the sky.

"Uh… this is so boring."

Stationed far from the port, where shipgirls rarely ventured, the Observer had only a sparse fleet for protection.

Not long after.

Buzz—

In the distance, a faint hum of engines grew louder, accompanied by small black dots on the horizon.

"Visitors?!"

The Observer's eyes lit up. She quickly activated her main cannons and led her fleet forward to intercept.

"Don't shoot!!"

"It's me!!!!"

The Purifier rode her shark-headed rigging, breaking through the waves.

"You?!"

The Observer blinked, puzzled at the sight of her fellow Siren.

High-ranking Sirens rarely crossed paths unless there was an emergency. Each was assigned to a specific sector.

"Captain—ah, no, Observer-sama. The commander asked me to deliver a message…"

"If you surrender to the port, boundless glory and wealth await…"

Dressed in her sailor uniform, the Purifier sidled up next to the Observer.

"???"

The Observer nearly toppled into the sea.

"Commander? Who? What nonsense are you spouting?!"

"Ahem—"

The Purifier cleared her throat, then began in an exaggeratedly formal tone:

"I, the Azure Lane Commander, sweep across the six directions, encompass the eight desolations. Shipgirls fall for me, the four corners of the world thrive under my rule… Now, the Starsea Alliance commands a million shipgirls, a thousand starships. What is your flickering firefly compared to the radiant moon in the sky?"

"Surrender with courtesy, and you shall retain your flagship title. A peaceful, prosperous world—what say you?"

"???"

"Where did you pick up this rap nonsense?!"

The Observer stared at the Purifier as if she'd lost her mind.

"Ahem, probably from some old archive."

The Purifier scratched her head and opted for a more straightforward explanation:

"A commander just arrived at the Azure Lane port. He's brought a fleet of space battleships to annihilate us."

"If we join him, we can eat well, drink well, and travel to other universes to fight aliens. If we refuse, well… he'll dismantle our riggings and toss us into a dark room to become plush toys."

"I thought about it. Fighting back and forth here is meaningless. Why not head to another world with him?"

She gestured toward the sky behind her.

"What's that?" The Observer squinted, only able to make out faint black dots.

"Turn on your radar."

The small girl complied, activating her radar system.

"Eh?!"

She nearly fell into the water again.

Suspended in the stratosphere were over thirty starships, looming over the sea like celestial sentinels.

Each starship was over a kilometer long, from battleships to space carriers. Their mere presence radiated an overwhelming sense of power.

They weren't something mass-produced Siren ships could ever hope to contend with.

"You brought the shipgirls here?!"

"You, with your thick eyebrows and big eyes, betrayed us too?!"

Observer was furious. Her location was classified; no one outside of her colleagues should have known about it.

"Look, the Tribunal Unit and the others are out of contact. There are only a few of us left in this universe. Why not join the port and explore other worlds together?"

Purifier continued her persuasive pitch.

"I refuse," the petite girl declared, crossing her arms.

"Unless they can defeat me."

"..."

"Ha? You brought this on yourself."

Aboard the Eternal Snowfall, Setsuna shook his head.

"All ships, open fire!!!"

Boom—

Smoke billowed, and waves roared as the ocean surface erupted in chaos.

...

One hour later.

Deep in another ocean on the opposite side of the Azure Lane world.

The Tester looked on in astonishment at the Purifier and Observer standing before her.

"You two? Why are you here? What's the matter?"

Ahem—

The two Siren shipgirls cleared their throats, then gestured toward the starships floating high above.

"The commander has a message for you…"

...

A week later.

As the Eternal Snowfall descended onto the aviation base of the capital city, shipgirls from both the port and the naval base crowded around in anticipation.

The air buzzed with excitement, every face glowing with hope.

They all knew that the Vanguard Fleet's mission to the Azure Lane world was to eliminate the Siren threat once and for all—an enemy they had fought for years without a decisive victory.

Now, with the advent of the space era and the massive boost in the shipgirls' power, there was finally a chance to claim total victory.

They waited anxiously for news from Setsuna and the expedition.

Click—

As the hatch of the Eternal Snowfall opened, Setsuna emerged first, flanked by several Heroic Spirits and the accompanying maid squad.

He scanned the sea of eager faces before waving to the crowd and speaking slowly:

"The Siren threat in the Azure Lane world has been completely neutralized."

"From this day forward, those seas will know permanent peace. There will be no more Siren interference. You can safely explore the far oceans and deep waters."

"We will soon dispatch Bulin fleets to collect resources and expand the port in that world, ensuring prosperity for both realms."

"Hooray—"

The gathered shipgirls erupted into a thunderous cheer, with some moved to tears of joy.

Years of war had finally ended, and it was a total victory for the port.

No longer would they need to fear sudden, inexplicable attacks while sailing the seas.

Some of the smaller shipgirls were already shouting, "Long live the commander!"

"Ahem, there's one more thing."

Setsuna cleared his throat, stepping aside to make room.

"I'd like to introduce some new friends. I hope everyone will get along well in the future."

"Hi~~ Azure Lane shipgirls, hello~~ I'm Purifier, everyone's old friend!!"

"We've fought for so many years, so let's get along from now on, okay~~"

The cheerful, sailor-uniform-dressed Purifier was the first to dash out, waving energetically and diving into the crowd of shipgirls.

"Wha??!"

"AAAAHHHH——"

"The Sirens are launching a surprise attack!!"

Several smaller shipgirls instinctively tried to flee upon seeing a high-ranking Siren. But before they could escape, Purifier wrapped them in her arms and began playfully rubbing their heads.

"Isn't this Tashkent? Hmm? I remember last year we had a little skirmish. I chased you over a hundred nautical miles across the sea. You were pretty quick back then."

"But you did throw torpedoes at me first, so let's call it even, okay?"

"And there's New Jersey. Tsk, you snuck in a shot at me with your cannons last time. I haven't settled that score yet…"

"Commander, help—"

A purple-haired destroyer squirmed helplessly as Purifier enthusiastically smothered her in a hug, ruffling her hair like a stuffed toy.

Meanwhile, more humanoid Sirens stepped out from behind Setsuna.

Observer, Tester, Omitter, and another white-haired girl in a white dress—Compiler.

Including Purifier, all five high-ranking Sirens of the Azure Lane world had gathered here.

"Ehhh?!"

A wave of commotion rippled through the crowd of shipgirls below.

"What's going on?!"

"Why are all the Sirens here?!"

Some of the high-ranking Sirens were familiar faces; others were entirely new to them. Despite being girls just like the shipgirls, the Sirens' pale skin, distinctive flags, and unique riggings set them apart.

How on earth had the Commander convinced them to switch sides?

"That other world has lost its purpose for observation and experimentation now that you've left, so we decided to come here."

The small Observer girl explained.

"But don't worry, we have no intention of being your enemies this time. According to our agreement with the Commander, we hope to undergo starship modifications and explore more unknown worlds."

"After all, the vast multiverse contains knowledge even our databases lack."

"Uh…"

The shipgirls' expressions were complicated. Their longtime adversaries, who they had fought tooth and nail, were now teammates. It was difficult to digest.

"You… aren't planning anything nefarious, are you?!"

Formidable's suspicious gaze swept over the five Sirens.

Purifier was cheerfully mingling with the shipgirls like an over-enthusiastic puppy, but the other four wore stoic expressions, radiating an air of detachment.

"In the past, my role was to observe your activities. Here, however, my focus will be on observing the Commander."

Observer replied calmly.

"He possesses the ability to pierce through dimensions and traverse the multiverse, making him far more valuable for observation and study than you all. Hmm…"

The petite Siren stepped closer to Setsuna, her tone serious.

"If possible, I hope to live with you, Commander, so I can conduct a comprehensive observation of your daily life—eating, combat, resting, uh, of course, sleeping too…"

"Considering we're of different species, perhaps we could even investigate the feasibility of producing offspring…"

Setsuna waved his hand dismissively.

"That's impossible. I can't produce mini-shipgirls with the shipgirls, so logically, I can't have mini-Sirens either."

"Is that so?"

Observer seemed a bit disappointed.

"???"

The shipgirls were aghast.

"You're plotting something after all!!!"

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