Crossover Shipgirls: Building a Dimensional Empire from Scratch

When it came to solving the problem of the Gastrea Virus in the little lolis, Setsuna considered many possible solutions.

First, there were a few individuals in the base who were highly skilled in magic—Lucoa, Tohru, and Mio.

Using magic, they could eliminate the virus and even heal the lolis’ injuries in the process.

However, this method was not efficient enough and was only suitable for saving children in critical condition.

With over three million little lolis to cure, it would take until the end of time at that pace.

If he wanted a large-scale solution, gene therapy was the only way forward.

...

Siren Naval Port.

Setsuna and Richelieu, accompanied by Enju Aihara, Midori Fuse, Tina, and a few other little lolis, were headed to see Compiler and Purifier.

As soon as they stepped into the dockyard, they were greeted by a bizarre sight.

Inside the massive berth, several Gastrea specimens were hanging from mechanical arms.

Each one was grotesquely shaped—some resembled enormous sea monsters, while others looked like mutated terrestrial mammals.

Judging by their classifications, these were at least Stage IV Gastrea, exceptionally powerful variants even in the Black Bullet world.

And yet, here they were, lined up neatly on the walls, displayed like trophies.

”Waaah—”

At the sight of the Gastrea, the little lolis immediately tensed up, instinctively grabbing onto Setsuna’s coat and huddling together.

Only after confirming that the creatures were truly, thoroughly dead did they finally relax.

Below, five Siren shipgirls from the experimental unit were gathered around a table.

Among them stood a woman in a messy lab coat, her hair completely disheveled.

She looked half-asleep, scribbling furiously in a notebook.

”Sumire Muroto?”

Setsuna suddenly recalled that she was a scientist from the Black Bullet world, an expert in Gastrea research.

Though, in terms of personal habits, she was notoriously sloppy.

”Oh, Commander?”

Hearing his voice, Purifier looked up and greeted him.

”When we were investigating the Black Bullet world earlier, we noticed she had quite the talent for biology. But later, Harbin ended up sending her off.”

”Tch, I figured dumping her in the Dragon Maid world would’ve been a waste. Someone like her—who has zero ability to take care of herself—might actually starve to death.”

”So I brought her back to study the Gastrea Virus. You don’t mind, right, Commander?”

Setsuna certainly didn’t mind.

If anything, he had nearly forgotten about her until Purifier brought her up.

Sumire Muroto’s presence was just that weak—when she had blended into the group heading to the Dragon Maid world, he hadn’t even noticed.

At the base, both the Sirens and shipgirls specialized in engineering and physics.

The Heroic Spirits and Spirits, on the other hand, focused on magic.

That left a gap in biological research.

Sumire’s intellect was at the highest level among humans—it was said she could read through an entire library in just three days and retain all the information.

But if left alone, she’d probably starve herself to death.

A genius in research, but a total failure in everything else.

He’d need to set up a proper lab for her in the future… and have Bulins take care of her.

”So? What exactly are you guys doing here?”

Setsuna glanced at the table.

On it were several porcelain plates, each containing slices of an unidentified meat with a strange, iridescent sheen.

”We’re studying the Gastrea creatures.”

Purifier answered with a guilty look.

”You mean by turning them into sashimi? You Sirens have some truly remarkable hobbies.”

Setsuna flicked Purifier on the forehead, then asked with curiosity:

”So… does it taste good?”

”It’s delicious! Purifier-chan just made it!”

Observer casually popped a slice into her mouth, nodded approvingly, and even gave a thumbs-up while handing a plate to Setsuna.

If one looked closely, though, her expression seemed slightly… off.

The rigging beneath her body even twitched a little.

The little lolis were absolutely stunned.

This was the first time they had ever seen someone treat a Gastrea creature like a snack.

Weren’t they afraid of getting infected?!

”…Seriously?”

Setsuna took a bite.

”...”

It tasted marginally better than Tohru’s tail meat.

Fortunately, after years of training, his poison resistance was maxed out.

”I don’t believe a damn thing you say!”

Wham—!

With a resounding bonk, he smacked Observer straight into the water.

Bubbles rose to the surface.

That one had terrible personality traits—she delighted in messing with people. Most likely, she had just fallen for Purifier’s prank and was now trying to drag someone else down with her.

The little lolis, already wide-eyed, trembled in silence.

So it wasn’t just the Sirens—even their Onii-chan was a total madman who ate Gastrea sashimi like it was nothing.

”...”

”...”

After doling out justice to Purifier and Observer, Setsuna moved on to the real reason he was here.

”Find a way to actually deal with the Gastrea Virus, ladies and gentlemen.”

”Don’t tell me you captured all these creatures just to eat them?!”

”...”

Compiler floated over on her jellyfish-like rigging, her ethereal voice echoing as she gazed at the three little lolis.

”May I extract some of your blood and conduct a few tests?”

”I need to perform a comparative analysis.”

”Onii-chan…?”

Enju Aihara, Midori Fuse, and Tina tugged at Setsuna’s coat.

The Siren girls weren’t as warm and friendly as the shipgirls or the Bulins. Their expressions were cold, and their outfits and rigging were all in muted, cool tones.

”Go ahead, it’s fine.”

Setsuna nodded.

Among the Sirens, Compiler was probably the most reliable. Aside from being a woman of few words, she had always quietly provided technical support.

Unlike a certain pair of troublemakers—Purifier and Observer.

With Setsuna’s reassurance, the three lolis followed Compiler into another room.

Inside, various instruments and devices were set up.

Some belonged to the Sirens for research, while others seemed to be Sumire Muroto’s—she had apparently been working alongside them for the past few days.

After the three girls lay down, Compiler conducted a full-body examination.

A strange scanning device from her rigging swept over them, and she extracted a vial of blood, placing it into an analyzer.

Two hours later, the results were in.

”The Gastrea Virus is a parasitic biological virus that can rapidly rewrite an organism’s genetic structure, transforming it into a Gastrea.”

”This process grants enhanced physical traits—greater size, increased speed, heightened reflexes, and more…”

”When combined with human DNA, it grants partial Gastrea-like abilities. For example, rabbit-type Infected exhibit incredible speed, planarian-type Infected have extraordinary regenerative abilities, and owl-type Infected possess enhanced sensory perception…”

”However, as time passes, the virus gradually increases its level of erosion. Once erosion surpasses 50%, the central nervous system is completely destroyed, leading to the total loss of rationality. The individual fully transforms into a Gastrea.”

Compiler drifted past the three little lolis, her voice calm and steady.

She handed a report to Setsuna.

Their current erosion rates ranged between 20–30%, meaning they had roughly three years left to live.

In the original storyline, many little lolis, unwilling to become monsters, chose to end their own lives.

Setsuna absolutely would not let that happen.

Whether through science or magic, there had to be a solution.

”The virus structure is not particularly complex. It can be eliminated through targeted therapy.”

Compiler stated matter-of-factly.

”After removing the Gastrea Virus, we can also isolate and replicate specific enhancement factors, enabling genetic modification in others.”

”For example, the dolphin factor could enhance intelligence, Enju Aihara’s rabbit-type factor could boost speed, and the planarian factor could greatly improve regenerative abilities…”

”It is even possible for an individual to receive multiple enhancement factors simultaneously.”

”Waaah—!!”

The three little lolis were ecstatic.

They had assumed that curing the virus would mean losing their special abilities.

It was a tradeoff they were reluctantly willing to accept in order to survive.

But to their shock, the Sirens’ technology was far beyond their expectations.

Not only could it remove the virus, but it could also preserve and extract their abilities for enhancement.

”So, does this mean I won’t just run fast anymore? I could be as smart as Chiharu Kashiwagi too?”

Enju Aihara tugged at Setsuna’s sleeve, her eyes sparkling with anticipation.

”What about me? I want a planarian factor too! That way, I won’t have to worry about getting hurt…”

Tina chimed in excitedly.

”I… I want a factor that lets me swim…”

Midori Fuse scratched her ear as she spoke.

”...”

Setsuna suddenly realized that his trip to the Black Bullet world had resulted in more than just acquiring lolis.

”…Are we about to ascend through genetic evolution?!”

”Uh… and the first ones ascending are the lolis?!…”

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