Crossover Shipgirls: Building a Dimensional Empire from Scratch

Setsuna assigned the task of curing the Gastrea Virus to the Sirens and Sumire Muroto.

According to Compiler and Purifier, even though the Sirens and shipgirls had invested all their technological advancements into engineering and physics, solving this problem wasn’t difficult for them.

Not to mention, they had a genius like Sumire Muroto working alongside them.

Every day, they shuttled between the Siren Naval Port and the city’s medical center.

Meanwhile, a massive operation was underway—thousands of Executor-class Sirens were dispatched to conduct blood tests on every single little loli.

With their white hair and golden eyes, the Executor-class Sirens carried specialized equipment, moving from dormitory to dormitory like census takers, ensuring that not a single child was overlooked.

Two weeks later.

Good news arrived from Sumire Muroto and the Sirens:

They had completely mastered the method to cure the Gastrea Virus.

Setsuna, along with Enju Aihara, Midori Fuse, and several other little lolis, arrived at the medical center.

This facility had only been officially put into use after the arrival of the Black Bullet world’s little lolis.

Before that, the capital had been home to shipgirls, Heroic Spirits, and Spirits—beings who either fell under the jurisdiction of engineering or simply never got sick.

The medical center itself was massive—its total area was over ten times that of a standard tertiary hospital.

However, the atmosphere inside wasn’t as cold and sterile as a typical hospital.

Its design followed the blue-and-white aesthetic of the port, and the presence of Bulins and Manjuus bustling through the halls added a lighthearted, welcoming touch.

Inside the wards, several children lay resting.

Some had erosion levels so high that they could no longer move freely.

Others were missing limbs or bore severe injuries.

The Cursed Children never suffered from conventional illnesses.

Every single one of their wounds came either from battles against Gastrea creatures or from the cruelty of human abuse.

Just like that one little girl whose eyes had been filled with molten lead.

Upon seeing Setsuna and Enju Aihara, many of the bedridden children struggled to sit up, forcing smiles as they greeted them.

They couldn’t run freely like their companions.

They couldn’t go to school or explore the wonders of this incredible city.

But at least… they were still alive.

Watching them, Setsuna and Richelieu felt a painful tightness in their chests.

”Every time I see them like this, I can’t help but think… the humans in that world were truly cruel.”

Richelieu clenched her fists slightly.

She knelt beside a little loli sitting in a wheelchair, her eyes wrapped in bandages, and gently tugged at Setsuna’s sleeve.

”Commander, why not call Mio and Tohru over? Maybe they could help. Lucoa should be able to do something too, right?”

”They’re already doing everything they can. But with so many children in need, I can only have them prioritize those in critical condition.”

Setsuna answered, gently patting the little loli on the shoulder.

”But don’t worry—if our progress in genetic biotechnology goes smoothly, you’ll all be back to full health soon.”

”Really? Thank you, Commander…”

The little loli gave him a bright, innocent smile.

They continued forward.

Soon, they arrived at a massive laboratory, where they found Sumire Muroto and several Siren shipgirls waiting for them.

Sumire Muroto’s dark circles had worsened—it was clear she had been pulling consecutive all-nighters.

Setsuna suspected that if the Sirens hadn’t been taking care of her, she might have already kicked the bucket.

Inside the spacious room, two rows of about sixty stasis pod-like devices were neatly arranged.

Each pod was connected to a computer-like terminal, its screen filled with scrolling lines of incomprehensible characters.

”We have successfully isolated a targeted genetic therapy that can completely eliminate the Gastrea Virus’s erosion on the human body.”

Purifier shook a vial of cyan-colored liquid as she spoke.

”At the same time, we’ve also managed to extract, replicate, and reassemble enhancement factors—effectively achieving a form of genetic ascension.”

”This formula was developed by Sumire Muroto, and the equipment was built by Compiler. Turns out we make a pretty great team…”

Setsuna nodded to both of them in acknowledgment.

Then, his attention was drawn to some peculiar text on the device screens.

[Loaded Enhancement Factor: (Not Selected)]

[Subject: (None)]

[Available Enhancement Factors: Rabbit-Type (5), Owl-Type (7), Cat-Type (6), Dolphin-Type (10), Planarian-Type (8)…]

A long list of different enhancement factors was displayed, each corresponding to a type of virus strain from either a Gastrea creature or a Cursed Child.

Every factor had a number in parentheses next to it.

”What’s this?”

Setsuna and Richelieu were both intrigued.

”A few days ago, when we conducted the large-scale medical examination and blood tests, we extracted and replicated the enhancement factors found in the children’s bodies.”

Purifier explained.

”This device allows us to install these enhancement factors into a human body, granting them the corresponding abilities.”

”Rabbit-Type enhances speed, Owl-Type improves vision and perception… Compiler probably already explained that part to you.”

”But—since these enhancement factors were originally derived from the Gastrea Virus, there’s one catch: they only work on girls.”

Compiler had mentioned separating the virus factors from the enhancement factors, and this was the result—

Stripping out the virus’s lethal components while preserving its useful biological enhancements.

”What do the numbers next to the enhancement factors mean?”

Richelieu asked.

”You can think of them like cost points.”

Purifier scratched her head.

”Each person has a different capacity for enhancement factors. Say, for example, a Rabbit-Type factor costs 5 points, and a Dolphin-Type costs 8—that means you’d need at least 13 points of capacity to install both at the same time.”

”For young children, the average capacity is between 10 and 15 points, meaning they can typically hold two to three enhancement factors.”

”Huh?…”

Setsuna suddenly had a very familiar feeling.

”…Wait a minute. This is literally just genetic ascension skill points, isn’t it?!”

By strategically combining different enhancement factors, a person could acquire multiple superhuman abilities.

Enhancement factors like the Dolphin-Type, which significantly boost intelligence, require a larger capacity—costing 10 gene points. After installing one, only a lower-cost factor could be added.

In contrast, standard physical enhancements like Rabbit-Type and Cat-Type take up less space—if squeezed in carefully, three different abilities could fit at once.

As for the gender restriction…

Setsuna didn’t see it as a problem. The entire base was filled with girls anyway.

And he had no need for genetic modifications himself—the Wisdom Cube’s physical enhancements were already ridiculous enough.

”Waaah—”

The little lolis accompanying him were completely stunned.

”Onii-chan, you guys are amazing…”

”So we’re not just getting cured—we can even gain a new superpower?!”

”Yep. Each of you pick one enhancement factor, but don’t go over your cost limit.”

Setsuna nodded.

Enju Aihara, Midori Fuse, and Tina thought it over carefully before each selecting one ability.

Setsuna also chose a Planarian-Type regeneration factor for a little loli in a wheelchair.

One by one, they were gently placed into the stasis pods.

Click—

As the glass seals locked into place, a white sedative mist filled the pods, gently lulling the little lolis into a deep sleep.

Whirr—

A robotic arm extended and injected them with the gene therapy.

On the monitor, their erosion rates plummeted sharply—until they reached 0%.

The Gastrea Virus was completely eliminated.

Then, with a low mechanical hum—

The machine administered the corresponding enhancement factor serum to each child.

The little loli who had been missing both legs began to regenerate before their eyes.

First, bone structure reformed.

Then, muscle fibers grew over the bones, followed by blood vessels and skin…

Within less than an hour, her legs had fully grown back.

This was the Planarian Factor, extracted from Hotaru Kouro.

Even injuries that would be instantly fatal to an ordinary person could now regenerate rapidly.

Click.

The anesthesia wore off, and the little loli slowly opened her eyes.

She stared at her new legs in disbelief.

On instinct, she reached out toward Setsuna, as if asking him to pick her up.

”You can stand now, you know.”

Setsuna crouched down beside her, smiling.

He held her hands, gently helping her up.

”Don’t be afraid—try walking.”

The little loli took a deep breath, slowly sitting upright.

Then, she cautiously placed a foot on the ground.

She hesitated, unable to believe she could actually stand on her own.

Step by step—

Her movements were unsteady at first, but as she walked forward, she gradually gained confidence.

Her pace quickened, her steps became smoother—

And finally, overwhelmed with emotion, she burst into tears and threw herself into Setsuna’s arms.

”Onii-chan… thank you!!!”

”Don’t cry, don’t cry.”

Setsuna knelt down, patting her back gently to comfort her.

”And now, you even have the Planarian Factor—your regeneration ability is super strong.”

”But that doesn’t mean you should do anything too dangerous, alright?”

”Mm-hmm… In the future, I’m going to be just like Enju Aihara and marry Onii-chan…”

The little loli sobbed, her face covered in tears.

”That’s way too early for you!!!”

”Go back and focus on resting and studying first!”

Richelieu sighed—part frustrated, part heartbroken—as she gently patted the girl’s head.

…

Before long.

Enju Aihara, Midori Fuse, and Tina also woke up one after another, sitting up in their stasis pods.

”Whoa…”

They could feel the subtle changes in their bodies.

The constant pain from viral erosion was completely gone, and in its place was a new ability.

Enju Aihara’s eyes wandered to a stack of research papers on a nearby table.

She had never studied anything related to biological sciences before.

She didn’t even recognize most of the equations and symbols in the documents.

And yet—

She could somehow understand bits and pieces of the content.

Almost on instinct, she picked up a few pages and began reading.

”Research on the separation of viral and enhancement factors in the Gastrea Virus—first, the viral factor is neutralized using a triple-targeted drug formula…”

”Wait, what? Why do I understand parts of this?”

”Ugh… even though there’s still a lot I don’t get? It feels like there’s a bunch of new knowledge in my head…”

The twin-tailed loli scratched her head in confusion.

”That’s the Dolphin Factor you wanted, remember?”

”The same one as Kayo Senju.”

Setsuna chuckled as he patted her head.

In the Black Bullet world, Kayo Senju had an incredibly unique superpower.

She was infected with the Dolphin-Type Gastrea Virus—her combat ability was weak, but her IQ surpassed 200.

For comparison, even Einstein was estimated to have an IQ of only 160.

This was a genius among geniuses—if trained properly, she could soon make groundbreaking contributions to scientific research.

”Eh? Onii-chan, didn’t my Gastrea Virus get cured?”

”Then… why do I still have ears?”

Midori Fuse stood in front of a mirror, tilting her head in confusion.

Her white cat ears still twitched on top of her head.

Before, due to her high erosion rate, she had already begun developing Gastrea-like physical traits.

”They’re already part of your body—it’s not like they can just shrink back in, right?”

Setsuna thought for a moment, then ruffled her hair again.

”Besides, isn’t being a catgirl super cute?”

”No one here is going to judge you for having cat ears… If anything, how about we find you some fellow catgirl friends?”

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