Crossover Shipgirls: Building a Dimensional Empire from Scratch

After most of the curious shipgirls dispersed, Setsuna, along with Richelieu, Yat Sen, and a few others, sat down in front of the Siren girls.

”Alright, tell me about yourselves.”

Leaning back in his chair, Setsuna got straight to the point.

”You’ve all been staying in the port for so long—we’re comrades at this point.”

”If there’s anything you need, just ask. As long as it’s within my power, I’ll do my best.”

He studied the Siren girls.

They had once been enemies of the shipgirls. But after years of coexistence, the Sirens had contributed greatly to the base—especially in research and development.

From FTL technology to the Starfall Spear and various new weapons, their efforts were indispensable.

The shipgirls had long since come to regard the Siren girls as friends.

However, because the Sirens usually kept to themselves, most people still didn’t know much about them.

Now that Compiler had helped Setsuna create a Navigator and spouted a bunch of strange things, it was clear they had a favor to ask.

”...”

Observer and Purifier exchanged glances and carefully opened their mouths.

”Commander, the Experimental faction’s mission is observation and experimentation—you understand that, right?”

”I told you this during our first meeting.”

Setsuna nodded.

One of the main reasons Observer the little loli had been lured over was because she found observing the multiverse and different civilizations more interesting than the endless mind games with shipgirls in the Azure Lane world.

”The port was one of our experimental fields, designated Beta Universe.”

Compiler spoke slowly and clearly.

”Our task was to observe shipgirl behavior there—and, when necessary, test technologies related to Wisdom Cubes.”

”Huh?”

Hearing that their home had originally been an experimental field, Richelieu, Yat Sen, Chen Hai, and the others looked a bit shaken.

”Wait—if the Sirens were running parallel universe experiments, doesn’t that mean there are countless versions of the port in Azure Lane?”

”Could I meet a shipgirl who’s identical to me in name, appearance, and power?”

Chen Hai frowned as she asked.

”You could have before—but not anymore.”

Observer shook her head.

”When the Commander appeared in the port, all the experimental fields collapsed into a ’singularity.’”

”Across countless observational experiments, you were the only variable—an outsider ’Commander’ from another world.”

She looked at Setsuna.

A Commander from another world had led the port down a completely unanticipated development path.

At first, their mecha-level tech was still within expectation. But then it escalated wildly.

New magic systems and technologies emerged one after another. Shipgirls were even lured into another world.

This had never happened before in all of Siren observation history.

—Who ever heard of the test subject escaping the world entirely?!

To put it metaphorically, the port was originally a cage with lab rats, observed from a higher dimension by the Sirens.

One day, the lab rat opened a dimensional gate and ran away on its own.

To the Sirens, Setsuna’s ability to pierce through different worlds was even more outrageous than their own parallel universe experiments.

After all, no matter how many alternate universes the Sirens played with, they couldn’t just open a portal to visit the Transformers or Abyssal Fleet universes.

”Oh...”

The shipgirls nodded thoughtfully.

Setsuna’s arrival had indeed changed the port’s trajectory drastically.

”So why did the Sirens create so many experimental fields?”

Yat Sen asked.

”According to Arbiter faction records, long ago the Sirens attempted space exploration, but were attacked by what may have been an advanced civilization—or a higher-dimensional existence.”

”It was overwhelmingly powerful and dealt a devastating blow to us, who had just begun stepping into space.”

”Since then, our technological development has been confined to the pre-space era—we’ve never touched the stars again.”

”Through observation and experimentation, we hoped to harness the power of Wisdom Cubes to find a way to fight that unknown enemy.”

Compiler projected several files.

Most were internal Siren documents, detailed records of what happened at the time.

”Oh, no wonder—you’re kinda like the Fleet of Fog.”

Setsuna rubbed his chin.

Technologically speaking, both the Sirens and the Fleet of Fog had clearly reached the interstellar era.

One had advanced space-time technology capable of parallel world observation and construction. The other was essentially starships in battleship skin.

The Fleet of Fog was limited by the Admiralty Code and couldn’t leave the sea.

The Sirens were blocked from the stars—unable to fly.

”After observing the Commander, we completely lost contact with the Arbiter faction and Dreamweaver. We couldn’t report anything back.”

”Perhaps during the collapse of the experimental fields, they became lost in some parallel universe.”

Thanks to Compiler and Observer’s explanation, Setsuna and the shipgirls gained a rough understanding of the situation.

The Experimental faction Sirens had followed him partly to continue their observation and research duties, and partly to figure out how to contact the Arbiter faction Sirens.

Unfortunately, they still hadn’t found any leads.

The Starsea Empire had advanced far beyond the Sirens in space tech.

But when it came to parallel universe traversal—space-time tech—there was nothing on the tech tree yet.

”Hmm...”

”Looks like I’ll have to figure out a way to unlock spatial tech and bring the Arbiters back.”

Setsuna jotted it down in his little notebook as a to-do.

Not exactly easy, but not impossible either. If tech wasn’t enough, there was always magic.

”Be careful—if you encounter that enemy, it could be a real problem. The Arbiters called it ’X.’”

Observer warned him.

”That’s not a big deal.”

Setsuna cleared his throat.

”There are plenty of ways to deal with powerful enemies in the multiverse. If we can’t win right away, we just power up and come back later. Sooner or later, it’ll be squashed.”

”This version of Earth doesn’t even have enemies—not even aliens. You’re free to explore space or hop universes.”

”If the Arbiter faction wants to come over, just move house. As long as they follow the rules, I’ll adopt them all.”

”???”

The Siren girls looked at each other.

This was the first time they’d heard of someone wanting to adopt the entire Arbiter faction.

A simple and brutally effective solution.

No matter how strong the enemy in the other world was, they could always just flee to this one.

With the Starsea Empire’s growth rate, a few more world visits and even the enemies they once couldn’t beat would be crushed like ants.

This was indeed a good place.

”Thank you. I’ll do my best to fulfill my duties.”

Compiler gave a slight nod.

”No problem.”

”That reminds me... I haven’t met any Arbiter Sirens yet. Don’t tell me they all look like you—lolis? I prefer them a bit older.”

Setsuna glanced at the little loli Observer and rubbed her head.

”Wah?!”

”Commander, even Sirens?! You’re shameless!”

The little loli opened her mouth and bit him.

”I was joking! Once we upgrade the Eternal Snowfall into a Juggernaut-class, I’ll reserve top positions just for you all, alright?!”

...

After the Siren girls helped him create Navigator TB, considering that the little one had no common sense and the fleet didn’t need her combat support just yet, Setsuna kept her by his side, raising her together with the shipgirls like a proper loli-rearing sim.

Administrative Center, main office.

The shipgirls were all doing their own tasks, assisting the Commander with paperwork.

TB sat on Setsuna’s lap, waving her tiny hands and tapping at the holographic interface on the desk.

”Papa… what’s this?”

Her tender, childish voice was unbearably cute.

”That’s a starship blueprint. Way too complicated for you.”

”Come on, let’s start with the basics.”

Setsuna ruffled TB’s hair.

He selected some Empire Starship Academy course materials from the holographic interface.

”This is the solar system, this is Earth, and right now we’re in Constantinople...”

”Where you are is called the Starsea Empire. The Empire currently spans the entire solar system, Alpha Centauri, and...”

”The capital is home to a variety of races—shipgirls, dragon girls, Spirits... You need to get along with them.”

Starting from the basics of the Starsea Empire, Setsuna began explaining. The little loli listened, her expression a mix of confusion and curiosity.

At birth, TB had received a wealth of knowledge on fleet command and tactics from the Siren database.

But when it came to daily life and everything outside of combat, she was a blank slate.

Pretty much like a newborn.

Fortunately, as an AI, TB had excellent perception and memory. There was no need for the messy process of teaching a toddler to talk.

Whatever Setsuna taught her, she could remember.

Even if she didn’t understand right away, she would figure it out eventually.

”After summer vacation, I’ll send you to school with the dark loli. You’ll probably finish elementary to high school in a year or two.”

Setsuna gave it some thought.

TB’s intelligence was on par with genetically enhanced super lolis, so there shouldn’t be a problem.

She could complete the basics in a short time, then enroll in the Starship Academy to learn more complex astrophysics, engineering, and so on.

He could offer far more than what her in-game raising system ever provided.

And when there was nothing else going on, he could take her on a tour of stellar bases and outer space.

”TB... doesn’t wanna go to school...”

”I wanna stay with Commander... Papa...”

The little loli hugged Setsuna’s arm, pouting and whining.

Every ”Papa” nearly melted Setsuna’s heart.

”My daughter’s too cute.”

”Be good, study well. I’ll come see you every day.”

”...”

TB looked around at the shipgirls in the room, then back at Setsuna.

Tilting her head, she put a finger to her lips and asked a question.

”Commander... is Papa... then who’s Mama?”

”???”

Before Setsuna could answer—

Shoukaku gently patted TB on the head.

”It’s me. I’ll take care of you like a mother would.”

”Woah...”

TB held Shoukaku’s hand in one and clung to Setsuna’s sleeve with the other, speaking in her tiny voice:

”Mama... Papa...”

”We’re a family...”

Then she walked up to Belfast, bowed, and greeted politely:

”Hello, Auntie!”

”???”

The head maid’s mouth twitched, nearly dropping the tray in her hands.

What is happening?!

Are you trying to stir up drama?!

Why is the Commander Papa, Shoukaku Mama, and I the Auntie?!

Aren’t we all oath-bound shipgirls to the Commander?!

Just because you give off peak waifu vibes doesn’t mean you get to scheme like this!

She quickly squatted down in front of TB and earnestly corrected her:

”I’m your Mama too.”

”Eh?!”

TB looked confused, turning to Setsuna for guidance.

”Uh, that’s fine too.”

Setsuna nodded, already anticipating what was about to happen.

”I’m your Mama too!!!”

”Call me Mama!!”

To avoid being labeled as ”Auntie” or ”Big Sis,” the harem members quickly swarmed around the little loli, battling for TB’s custody rights.

It looked exactly like some melodramatic soap opera airing during prime time.

At first, TB could still keep track of who was who.

Calling the older aircraft carriers and battleships ”Mama” wasn’t a problem.

But when she saw Nagato—whose height was about the same as hers—she couldn’t take it anymore.

”Why does Papa get to have so many Mamas?!”

”No! You can only be my little sister or big sister!”

”???”

Lady Nagato was emotionally devastated.

”I—I’m clearly the Commander’s oath-bound ship! If you’re calling him Papa, why can I only be your sister?!”

”Isn’t this family tree getting a little ridiculous?!”

”Didn’t you also call the Commander Papa last night? You can each have your own logic.”

Chen Hai didn’t seem bothered at all.

”???”

...

After handing TB over to be raised in shifts by the shipgirls, the stir caused by the Siren-made little navigator finally died down.

She still carried many mysteries, clearly tied to the missing Dreamweaver and the Arbiter faction. Setsuna added all of it to his growing list of reminders.

”Parallel universe traversal tech, huh... that’s going to be a pain.”

Setsuna looked at the star map, recalling what Compiler had said.

The worlds he saw in the Hyperdimensional Star Map were all large-scale universes.

Some of those larger universes were themselves composed of countless smaller sub-worlds.

Like the dual-world structure in the Dragon Maid universe—modern civilization and magic world—or how the Transformers universe was a separate one entirely.

Even the Azur Lane universe contained numerous parallel timelines. Due to Setsuna’s arrival as a ”singular” Commander, they had all collapsed into the current Port world.

Dreamweaver and the Arbiters were likely scattered across other parallel universes.

Finding and reuniting them with Observer and the other Sirens wouldn’t be easy.

Though the Sirens lacked aerospace capabilities due to their confinement, their space-time tech had advanced quite far.

They developed things like mirror seas and alternate realities. In a way, their tech tree was seriously skewed.

”Whatever. I’ll gradually unlock the tech tree and bring you all back.”

”Kayo, I’ve got a new assignment for you.”

Setsuna contacted the lolis at the Research Institute and assigned them a new field of study—parallel universes and spatial traversal.

”Ooh, sounds like a challenging topic. We’ll do our best.”

The blonde loli on the holographic display nodded.

”Let’s start with theory. Once we’ve built the framework, we’ll test its feasibility.”

As Commander, he didn’t need to get involved in the research details—that was for the R&D department.

If the science lolis needed reference material, he’d just go fetch it from another world—same as he did with FTL tech.

After assigning the task, Setsuna turned his gaze to a few neighboring worlds on the star map.

”Dimensional cooldown’s almost done. Let’s see where to go next...”

”Three-Body... KonoSuba... tch, better wait until ship refits are complete.”

After browsing for a while, his eyes settled on the Uma Musume world.

Since the Eternal Snowfall was undergoing upgrades, it wasn’t a good time to visit a dangerous world. This peaceful one was just right.

”Alright, let’s go. Time to add some species diversity. Let’s grab a few horse girls to ride.”

”And maybe blow their minds with a bit of gene ascension.”

...

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