Crossover Shipgirls: Building a Dimensional Empire from Scratch

”Iron Blood First Fleet reporting: The Southern Hemisphere continent, totaling 12 countries, has been pacified. 9 surrendered, 3 were purged.”

”Eagle Union Second Fleet reporting: All western nations and 8 subordinate free city-states have been fully pacified.”

”Iris Libre Fleet reporting: All island tribes have been pacified. Total enemies eliminated...”

Aboard the Eternal Snowfall, Setsuna listened to the victorious reports coming in from all corners of the world.

Every ruler who had received a declaration of war was met with a dispatched fleet sent to conquer them.

The feudal-era natives had weak combat power, but their fragmented civilization made conquest slightly more troublesome.

Fortunately, with hundreds of shipgirls in his fleets, summoning any one of them could wipe out entire regions.

On the main control console, Setsuna projected a hologram of the Akame ga Kill world. With each conquered nation, he marked it red on the globe.

The red areas increased rapidly, and the coloring progressed faster and faster.

Finally, two days later—

When the last expedition fleet returned with news of total surrender,

A system prompt followed.

[No independent resistance remains in the Akame ga Kill world. All civilizations and nations have surrendered.]

[Interdimensional War complete. Victor: Starsea Alliance]

[Interdimensional portal has closed]

At the same time, the spatial rift above the Imperial Capital, which had remained open, slowly sealed shut.

Ironically, the portal of the interdimensional war had always been two-way—allowing both worlds to freely invade one another.

But since Setsuna’s fleet had arrived, they crushed all opposition in a sweeping, one-sided conquest.

The feudal natives never even had the chance to counterattack.

Even if they wanted to use the portal to invade Setsuna’s world, a guard fleet was stationed at the gate.

On the other side of the portal—in their capital city—a few bored Siren girls had been waiting for days.

Observer and Purifier spent their time lounging in the sea, staring at the portal, eager for someone to jump through and be captured.

They wanted to dissect a few alien lifeforms for study.

Unfortunately, the Akame ga Kill world lacked such capability.

So, although in theory it was a mutual war, the overwhelming technological gap had turned it into a one-sided invasion.

”Interesting. I nearly forgot the portal was two-way.”

Setsuna chuckled.

”These natives have been beaten nonstop. It didn’t even feel like a real war with any back-and-forth.”

Then—

A window popped up in front of him like a battle report screen.

[Congratulations to the host for winning the Interdimensional War. Calculating spoils of war...]

”Oh?”

When conquering other worlds, the most exciting part was always collecting the loot.

Previously, he always looted it himself. This time, it was system-issued.

He was eager to see what kind of rewards the Interdimensional War would yield.

[Acquired Authority: None]

[This world is a purely technological civilization. No divine or transcendent entities exist.]

”...”

Setsuna wasn’t surprised. This world had no concept of gods.

[Acquired Spoils: All unique technologies from the Akame ga Kill world]

[Including blueprints and prototype models of all 48 Teigu and all Shingu]

Boom—

Suddenly, his storage space was filled with a mountain of items.

Setsuna pulled them out to take a look.

First were several thick stacks of documents:

Blueprints, manufacturing methods, and production requirements for every Teigu.

As expected, victory in the Interdimensional War allowed total tech plundering.

Even if the secrets of Teigu creation had been lost, the system provided complete instructions.

Then came various Teigu in the forms of swords, guns, cannons, scissors, and more.

The Akame ga Kill world had a total of 48 Teigu, plus countless Shingu.

The system delivered every single one of them to Setsuna as spoils of war.

He casually pulled them out one by one, tossing them to the ground. Soon, a small mountain of Teigu had formed.

Night Raid and Esdeath were left utterly speechless.

”One-Cut Killer [Murasame]? Oh, is this Akame’s sword? The system sent me another copy?”

”Roman Artillery [Pumpkin]? Mine’s Teigu? Doesn’t seem as good as a supergravity cannon...”

”Demon God Manifestation [Demon’s Extract]? Same model as Esdeath’s?”

”Dimensional Formation [Shambhala]... a teleportation Teigu? Now that has some research value...”

”Wait!! What are you doing?! Where did all these come from?!”

Akame, Mine, Esdeath, and the other locals were stunned.

There was no mistaking it—the items Setsuna was pulling out were Teigu, and they were exact replicas of their own!

The original founder of the Empire had only ever created 48 Teigu. They had never heard of any copies.

Later emperors had tried to recreate them, but failed. The weaker imitations were called Shingu.

”Murasame?! How do you have Murasame?!”

Akame crouched down and picked up the black katana.

It was identical to the one at her waist. No visible differences.

Sensing it closely, she could feel the same dangerous aura unique to genuine Teigu.

These weren’t fakes or replicas—they were real!

Esdeath held the jar of blood, just as confused.

Her ice-controlling powers had come from drinking the blood of a super-dangerous species, supposedly extinct.

Yet this jar overflowed with the same killing intent. Genuine.

”Commander, what is this?!...”

The other members of Night Raid also found replicas of their own Teigu.

They compared them side by side in disbelief.

No matter the shape or the energy within, the copies were completely identical.

Gudako, Artoria, and other Chaldea Servants were also surprised.

Artoria picked up an ornament-shaped Teigu.

”Dimensional Formation [Shambhala]? I remember this belonged to the minister’s son, Syura. I accidentally destroyed it with Excalibur during our fight...”

”Master, where did you get all this?!”

Nero rummaged through the pile and pulled out a glove-shaped device.

”Hmm, is this Perfector ? I think I wrecked it during my duel with Dr. Stylish?”

The Servants’ Noble Phantasms were incredibly destructive.

During fights with Teigu users, they often vaporized both the person and their Teigu, leaving nothing behind.

It had been disappointing not to collect trophies at the time.

Who would’ve thought the system would provide even those that had been destroyed?

”The National Defense Machine God?! How do you have this too?!”

Finally, Najenda saw Setsuna pull out a massive black mech and lost her composure.

It was a gigantic armor-type Teigu, similar in size to Gudako’s Barbatos.

Boxy and formidable, it barely fit inside the spacious Eternal Snowfall.

Even just staring at it from below left Night Raid feeling uneasy.

[National Defense Machine God: Shikoutazer]

Forged by the Empire’s first emperor, it was the most powerful of all Teigu—the origin of them all.

The Supreme Teigu could destroy entire nations. Legends said it had godlike power.

But only those of imperial blood could wield it.

It was both the pinnacle and the genesis of all Teigu, only used in dire circumstances.

Its immense power had a cost: it could drive its user mad with bloodlust.

”Interesting...”

Setsuna looked over the pile of Teigu and schematics.

Of course he knew they were real. The system wouldn’t hand him counterfeits.

But this kind of brute-force loot drop method still surprised him.

Just as the Interdimensional War’s reward description said: the victor gained all unique technologies, magic, and authorities of the defeated world.

Since the Akame ga Kill world had no magic or deities,

The only ”special technology” was its Teigu and Shingu.

Even those that had been destroyed were replaced by the system.

”So everything valuable in the Akame ga Kill world is right here?”

Setsuna flipped through the schematics.

Every detail was included—

From Teigu and Shingu forging instructions to raw material composition and atomic breakdown.

[Yes. As the reward for the conqueror, you are entitled to everything from the opposing world.]

...

A few hours later.

In the main control room of the Eternal Snowfall, the shipgirls from all major expedition fleets had gathered.

Even Observer and Purifier, who had been stationed at the capital, were teleported over via anchor points.

”The war is over. We’ve completely conquered the Akame ga Kill world.”

”These are the spoils.”

Setsuna gave a concise briefing.

”...”

”These are the rewards from the interdimensional war?”

The shipgirls stared curiously at the pile of Teigu.

”Yes, this is everything of value in the Akame ga Kill world.”

Setsuna nodded.

He had started to understand the mechanism of interdimensional war.

As long as you win, you get everything from the opposing world.

If they are a tech-based civilization, you receive all their unique technologies. If they are divine, you plunder their authorities.

Even lost knowledge would be automatically restored by the system.

Of course, this kind of action came with great risk.

It declared war on the entire target world.

The Akame ga Kill world was just a group of natives. No aliens, no gods. Conquering it was trivial.

But if a war were declared on a world like Stellaris, they would face a sea of space civilizations, fallen empires, swarms, higher-dimensional demons, and extermination protocols.

Declare war on the Warhammer universe, and the Four Chaos Gods plus the Emperor would come punch you.

Total chaos.

Once Setsuna’s power was high enough in the future, interdimensional conquest would be an incredibly efficient method—

The simplest and fastest way to drain an entire world of value.

—As long as you didn’t lose.

Since the war was two-way, if the enemy flipped the tables, they could plunder your world too.

Setsuna only wanted to loot alien tech—not get looted.

”A total of 48 Teigu, including prototypes and manufacturing methods, as well as some Shingu.”

”Take a look and see if there’s anything useful.”

”We can have Engineering start mass-producing Teigu in the future.”

He gestured toward the pile.

”Wait, mass-produce Teigu?!”

Esdeath and Akame were dumbfounded.

They couldn’t understand Setsuna at all.

Something that others fought over and killed for—in Setsuna’s hands, it was just a cheap mass-production item.

”Is that strange?”

Setsuna turned to look at the Night Raid squad.

”Teigu are nothing more than tools forged by the Empire’s craftsmen, using secret techniques and materials from Danger Beasts and Orichalcum.”

”In terms of tech, the Bulins are on a different dimensional level from those craftsmen. In terms of materials, we have everything. As long as we know the elemental composition and molecular structure, anything can be synthesized.”

”Reverse-engineering native tech with spacefaring civilization tools? That’s supposed to be hard? You didn’t spec into Celestial Engineering for your ascension path, did you?!”

As he spoke, he waved to summon a Purple Bulin.

Handing her the blueprint for Murasame, he asked:

”Can you make this?”

Setsuna rubbed the little Bulin’s head.

”...”

Purple Bulin flipped through a few pages, then immediately looked up.

”Burin!”

”Commander, this is just a cold weapon! Bulin can make it in half an hour, purin!!”

”You heard her. If Bulin says she can, then she can.”

Setsuna snapped his fingers.

”Go prep the materials for Bulin.”

Half an hour later,

Purple Bulin got to work right on site. Holding her giant wrench, she began hammering away at the Orichalcum.

Coincidentally, the Heroic Spirit team had just finished hunting some Danger Beasts, so they handed those over too.

Zzzzz—

Bang bang bang bang—

Bulin’s actions were so fast, they dazzled the onlookers.

It was Akame’s first time seeing someone forge a sword using a wrench.

She didn’t understand it—but she was thoroughly shocked.

A huge chunk of metal twisted and transformed under Bulin’s hammering.

Then she mixed in the Danger Beast materials.

After a series of utterly physics-defying stretches and transformations,

The lump of metal became a brand-new longblade.

”Finished, buli!”

Purple Bulin handed the newly forged Murasame to Setsuna.

It looked exactly like Akame’s, and the system-awarded one too.

When mixed together, you couldn’t tell them apart.

”Mm... here, take it.”

Setsuna inspected it briefly, then casually handed it to Kanae.

”Later, make one for Shinobu, Kanao, and Nezuko too. This thing should be a bit better than a Nichirin Blade.”

The Demon Slayer team was used to Nichirin Blades, but outside their world, there were no demons to slay.

[Murasame] was still more effective against ordinary human enemies with its instant-kill ability.

”Thank you, Commander!”

Kanae was overjoyed and quickly bowed.

It was the first time she had received a gift from Setsuna. Even if it wasn’t especially valuable, it made her very happy.

”...”

Akame looked at the three Murasame blades, opened her mouth, and didn’t know what to say.

The weapon she was most proud of, her ultimate trump card Teigu,

Had just become a mass-produced item made by a loli with a wrench in thirty minutes.

The entire Night Raid team began questioning their lives.

After witnessing Bulin’s half-hour Teigu-forging display,

Everyone’s attention returned to the pile of war spoils.

They began reading the manuals, picking through the lot.

Since Teigu could now be mass-produced, it was necessary to pick out the most valuable ones.

Flame-throwing, electric-blasting, and other flashy Teigu weren’t very useful.

They might be cool for tricks, but in terms of power, Noble Phantasms and shipgirls’ naval guns vastly outclassed them.

Transforming armor Teigu also didn’t interest Setsuna much.

He compared the likes of Demon God Manifestation, Demon Armor, and others with Gundams.

The conclusion: they couldn’t even beat Gudako’s Barbatos, let alone his own Turn A...

In the end, only the more utility-focused Teigu stood out.

”Dimensional Formation [Shambhala] — a spatial teleportation Teigu that can instantly move the target to a specified location.”

”Not sure if it can cross dimensions yet, but with a few modifications, it could be great for short-range mobility.”

Soon, Yat Sen discovered something valuable.

Teleportation was universally useful.

Outside of a few spell-savvy elves and dragon girls, no one at the base could use teleportation magic.

Even the fastest shipgirls relied on engines. Spatial transfer was a different level entirely.

Plus, Dimensional Formation could teleport not just the user, but others too.

”Alright, take it back to Engineering. Definitely worth mass-producing.”

Setsuna nodded.

”What about Demon God Manifestation [Demon’s Extract]? The blood of a Super-Danger Beast, like Esdeath drank? Maybe it can give others abilities like hers?”

Taihou tilted her head.

”Send it to Life Sciences. It’s biotech, not Bulin’s department. Let’s see if Sumire Muroto can extract the active component.”

Setsuna figured Esdeath’s Teigu was different from the rest.

Her personality—was it nature or the influence of the Teigu? Still uncertain.

”Phantasmagoria [Gaia Foundation] — Commander, this one is fun!”

Gudako hugged a makeup-box-looking Teigu.

”Lets the user transform into anything they want. Shapeshifting?!”

”Aside from assassination and hide-and-seek, what good is it? It doesn’t even fool radar, right?”

Richelieu stared in confusion.

”No, it’s different.”

Gudako clung to the Teigu possessively.

”You oath-bound shipgirls don’t get my pain. I could use this to become another shipgirl, sneak into the Commander’s room...”

”Turn the rice into cooked rice, and make him accept me as his woman...”

”He’s not the type to deny responsibility after taking advantage of an innocent girl, right?!...”

”???”

The shipgirls stared at Gudako, speechless.

Bonk!

Setsuna thumped the Human Evil on the head, sending her into a crouching defensive stance.

”You little genius. With that personality, you couldn’t impersonate any shipgirl even if you tried.”

”What does that matter?!”

Gudako grumbled, rubbing her head.

”In the future, no matter who you want to—uh—do, I can become them for you! Isn’t this Teigu super handy?! It can fulfill all your desires!”

”Not just shipgirls, Spirits, and Heroic Spirits—you want furries or aliens too? I can do that!”

”???”

”How the hell do you even come up with that kind of use?!”

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