Crossover Shipgirls: Building a Dimensional Empire from Scratch

After establishing a new kind of sustainable resource exploitation in the Goblin Slayer world, its complete conquest was declared.

From now on, it was enough to have the dragon girls and shipgirls periodically bring teams over to harvest a fresh wave of monsters.

In the administrative center, Setsuna casually opened the statistical panel he hadn't checked in a while.

[Civilization Overview]

• Civilization Type: Technological Civilization

• Technological Level: Space Age (Sub-light Speed)

• Population: 17.323 million

• Species: Humans, Shipgirls, Sirens, Dragons, Catgirls, Heroic Spirits, Spirits, Synapseans, Mechgirls

"Whoa?"

The population had grown even faster than Setsuna had expected.

Before heading to the Akame ga Kill world, it was under 10 million. Now it was pushing 20 million.

The vast majority were Bulins and Angeloids.

Both combat and domestic model Angeloids were counted. Each shipgirl's ship carried anywhere from hundreds to thousands of Angeloids.

Bulins could create more Bulins through Bulin fusion, and Angeloids could self-replicate.

Once a basic population was established, their unit production rate was staggering.

All of them were top-quality labor and combat units—the more, the better, as long as resources held.

When it came time to develop interstellar resources, they'd need hundreds of thousands, even millions of Bulins and Angeloids to build infrastructure on untamed planets.

"Been stuck at sublight tech for a while..."

Setsuna pondered.

Faster-than-light technology had been bottlenecking progress, but fortunately, he'd brought back the Transwarp Key from the Transformers world.

He believed it wouldn't be long before the research lolis in the stellar base delivered some good news.

Once they broke the light-speed barrier, their civilization would enter a whole new stage of development.

"We're basically an AI civilization, aren't we?"

Richelieu remarked dryly.

"I used to think that bringing in 3 million lolis made the 1:1 ratio of Bulins to lolis in the capital quite nice."

"Now the loli population is just a rounding error compared to the Angeloids and Bulins..."

"Isn't that a good thing?"

Setsuna grinned.

The lolis handled research, the Bulins ran the industry, and the Angeloids handled chores and combat.

All of them were high-quality citizens.

No crime, no stability issues, and even minimal resource consumption—the Angeloids used internal reactors for power, didn't need food or rest.

Bulins occasionally snacked, but most resources went to supporting the lolis and a few regular humans.

For a civilization with multiple vassal worlds, this was effortless.

Their standard of living had essentially reached utopia.

"..."

Richelieu found the image of future planets across the galaxy being populated entirely by Bulins a bit surreal.

Sort of... cute, maybe.

Swipe—

Setsuna opened the starmap again.

"Next... while Kayo Senju and Purifier are researching tech, we can handle something else."

"Let's take care of this world."

"Hmm?!"

Hearing of another expedition plan, everyone leaned in.

Among the second batch of discovered neighbors, only one world remained unconquered:

Overlord (Tier-II Magic Age)

A rather intriguing world.

It centered on a super-popular online game from Earth: YGGDRASIL.

On the day the game's servers were shutting down, a young man named Suzuki Satoru stayed in his guild, waiting to be forcefully logged out.

But even after the shutdown time, he couldn't log out—the world had glitched.

In his avatar form, a powerful skeletal mage named Ainz Ooal Gown, he and his entire guild were transported to another world.

The NPCs had suddenly gained independent thought, and the guild led by Ainz began stirring up events in this new world.

Overlord was a classic medieval fantasy world.

It contained all kinds of magical systems.

Setsuna felt it was time to balance the disparity between his tech-side and magic-side developments.

"Is this another world similar to Goblin Slayer? Do they have no gods? Are we sending a fleet for the conquest?"

Yat Sen inquired.

"..."

Setsuna paused for a moment.

"No, I'm planning to launch another Interdimensional War—to completely conquer the Overlord world."

...

Two hours later.

The administrative center was once again packed with shipgirls, dragon girls, Spirits, and other allies.

"This time, our conquest target is the Overlord world."

"We plan to initiate an Interdimensional War against the Overlord world, just like we did with the Akame ga Kill world."

Setsuna stood on the podium and began his briefing.

"Ohhh?!"

The shipgirls and Heroic Spirits below started chattering excitedly.

An Interdimensional War was different from ordinary traversals—it was a full-scale conflict between two worlds.

The victor could seize everything from the opponent's world.

During the conquest of Akame ga Kill, the system handed Setsuna the full set of Teigu, Shingu, and blueprints—even ones previously lost to history.

As long as you won, you could plunder anything native to that world, even divine authorities and powers.

Of course, the risks were massive.

Nearly all forces in the target world would unite to resist the foreign invaders—unless you could find collaborators.

"Master, let me go with you."

"I'll burn all your enemies to ashes."

Jeanne Alter spoke with conviction.

As a member of the harem now, she felt it was only natural to accompany her Master to battle in other worlds.

"Me too, me too! I wanna be on the frontlines!!!"

Gudako and others eagerly raised their hands.

The thought of fighting strong foes from another world made everyone's eyes light up.

Setsuna gestured for silence.

"Richelieu."

He looked toward his secretary ship.

Richelieu and some Angeloids brought over a stack of documents and swiftly distributed them.

They included setting details of the Overlord world, the original novel, faction divisions, power systems, and more.

They also projected several Overlord video clips on a holo-screen.

Everyone studied the information seriously, analyzing the strength of potential enemies from the smallest martial techniques to the most advanced tier spells.

They left no detail unchecked—information advantage meant everything in war.

"The protagonist in this world is undead... that's a surprise."

"They count as evil beings, right? That's a bit much..."

Yat Sen frowned.

The Great Tomb of Nazarick was filled with -300 or -500 morality characters—evil or chaotic evil alignment.

Many despised humans, treating torture and cannibalism as routine.

Not to mention Demiurge's human livestock farm.

Even the Sorcerer King himself was no exception.

To them, humans were low-level beings, mere test subjects or food.

From the Sorcerer King's perspective, that was normal.

But looking around at themselves—and at their ordinary human companions and the base's many little girls—the shipgirls couldn't ignore the racial issue between humans and undead.

"I hate undead and skeletons."

Tohru narrowed her eyes at the Sorcerer King.

"No meat at all. They're tough to chew and stink of rot."

"???"

"You're a chaotic evil dragon, and you have the right to talk?!"

Elma, sitting beside her, was dumbfounded.

She took issue with Tohru's habit of judging others based on edibility.

"Hmph, I'm the Commander's maid now. I'm not some evil dragon..."

Tohru pouted, squirming cutely.

The two dragon girls bickered for a bit.

Richelieu suddenly remembered something.

"Commander, didn't you say the victor of an Interdimensional War not only gets gear and data, but also gains divine authority?"

"The Overlord world may not have high-tier gods, but the Great Tomb of Nazarick came from the game YGGDRASIL. Would winning make us... administrators?!"

"Yes, I've had similar thoughts. That's one reason I'm starting this Interdimensional War."

Setsuna nodded.

There was no divine authority to plunder in the Akame ga Kill world, but in the Overlord world, it was worth a try.

The Sorcerer King always worried about stronger beings or other players and invaders.

Now, his imagined nightmare was about to become reality.

After confirming that the Overlord world would be conquered via an Interdimensional War, the base quickly began planning the expedition and selecting participants.

The Overlord world was far larger and more powerful than the Akame ga Kill world.

It lacked a unified global government, with numerous distinctly different nations spread across the planet.

"If we want to conquer the entire world, we'll need to take over every faction and nation in it."

"This time it'll be a bit more complicated. In addition to human nations, there are several non-human species."

Setsuna and Richelieu projected a map of the Overlord world.

Its factions were diverse. Human nations like the Re-Estize Kingdom, Baharuth Empire, Slane Theocracy, and Roble Holy Kingdom dominated most of the continent.

There were also non-human countries and organizations—like the Lizardman tribes and the Frost Dragons in the Azerlisia Mountains.

Scattered throughout the land were some powerful individuals.

The average strength of human kingdoms wasn't high. Their tech level was roughly medieval, with only limited use of magic.

They mostly relied on regular soldiers, low-tier magic casters, and adventurers.

Truly powerful humans were rare—each nation had only a handful at most.

For instance, Baharuth's court mage Fluder, Slane Theocracy's Black Scripture, and the Re-Estize Kingdom's Warrior Captain.

"The average strength of human kingdoms is low. Like in the Akame world, a fleet should be enough to subjugate them."

"If they aren't stupid, they should realize the power gap between us."

"Watch out a bit for the Slane Theocracy's Antilene. She's tougher than the others."

Setsuna assigned several shipgirls their tasks.

"As for the lizardmen, dragons, and other races... who wants to handle them?"

"Me, me, me!"

Tohru raised her hand instantly.

"They have dragons too? Let me go see, Commander."

"Alright."

Setsuna thought it over and handed the mission of subduing the non-human races to Tohru.

Dragons had a natural dominance over other species.

Most dragons in the Overlord world were around level 40–50—mid-tier strength.

The strongest—like the Platinum Dragon Lord, Color Dragon Lord, and Dark Dragon Lord—were on par with the Floor Guardians.

But they still didn't compare to a demigod-level dragon like Tohru.

After assigning the various world factions, the main focus turned to the Great Tomb of Nazarick.

This was the core of the Overlord world—the single strongest force.

Any monster from that tomb could wipe out a human kingdom. With an average level of 100, the Floor Guardians and the Sorcerer King himself were comparable to gods-level beings in this world.

"Hmm, it seems we don't use levels like they do? Their system makes power scaling so much easier..."

"It's hard to evaluate strength on our side..."

Richelieu examined the Overlord setting.

In a game world, levels made power clear at a glance.

Level 40–50 meant top-tier strength. Nazarick had loads of level 80–90 and even 100 monsters.

Their own system was more ambiguous—there were no stats, and strength was judged by actual combat.

"Um, Commander, if we convert it—what level would we be in the Overlord world?"

"What kind of enemies could we challenge?"

Kanae and Akame asked cautiously.

"Hah?"

Setsuna looked at the two, amused, and thought for a moment.

"You're probably over level 30. With your Teigu and genetic upgrades, you're definitely considered strong in a human nation."

"If we go by Adventurer rank... you'd be at least Mithril class."

"Alright, then let's go fight humans."

The Night Raid and Demon Slayer teams were thrilled to be acknowledged.

They decided to find evenly matched opponents—they knew they couldn't handle demons and monsters, but practicing against humans was perfect.

"Husband, what about me?"

Mio tugged at Setsuna's sleeve, asking curiously.

"You?!"

"Weren't your stats in the Date A Live world all 999s, full SSS panels—basically a walking cheat?"

"In the Overlord world, you'd probably be one of those ??? monsters with a skull icon."

Setsuna was amused by the Spirit of Origin.

He looked around at the others with interest.

There were quite a few overpowered members on their side.

By comparison, most would be max-level monsters.

"..."

"Commander, I have a question."

After the assignments were mostly done, Richelieu paused.

"If we want to recruit allies in the Overlord world, Antilene, Evileye, and the Holy Queen should be relatively easy."

"But what about Albedo, Shalltear, Narberal...? They're all undead, right? Recruiting them would be tricky, and their personalities and lifestyles are... not quite compatible with ours..."

As the secretary ship, Richelieu knew Setsuna well.

She understood that whenever he led a expedition, he usually brought back a few interesting girls.

She often helped arrange that.

As a senior, she saw the newcomers as juniors, carrying a sense of main-wife superiority.

But this time, Richelieu found it a bit thorny.

The Floor Guardians and Pleiades were NPCs created by former players, loyal to Nazarick.

Expecting them to betray their creator was unlikely.

Many of them even looked down on humans.

Shalltear saw humans as food, and most of the Pleiades viewed them as inferior beings.

Getting along would be a challenge.

"Maybe we could capture them first, then slowly try to reform them?"

Jeanne d'Arc suggested tentatively.

"That's nice of you, but seriously, they're undead. Do you even know what Shalltear and the Pleiades are like?!"

Jeanne Alter scoffed.

"Even if you captured them, be glad if they don't self-destruct. Reforming them? In your dreams."

"Tch..."

Setsuna leaned back in his chair, deep in thought.

He did want to get Albedo and the Pleiades.

But in practice, it would be difficult.

Convincing an NPC set to be 'loyal' from the start wasn't going to happen.

If necessary, eliminating them was also fine.

"Hmm..."

"Use the spiritron transfer device? Have Mio think of something? Or go to the surface world of Overlord and kick Suzuki Satoru offline early?"

"Maybe pay Suzuki to become a normie and hand over admin rights to me?"

He ran through a few ideas.

There were options—it was just a matter of how difficult or easy they were.

"Wait."

"Since Albedo and the Pleiades were created as NPCs in a game, there should be another way..."

Even if he recruited them, hearing them constantly prattle about their creator and the other Supreme Beings would be annoying.

He had nothing to do with those players.

"Hmm... hold on?"

Suddenly, he thought of something.

[Interdimensional War]

This ability's description allowed total invasion of a target world until one side was either eliminated or surrendered.

The victor could claim all of the target world's technologies and authorities.

The focus was on stealing the opponent's tech, equipment, and world authorities—basically looting everything of value.

The Akame world didn't have authorities to steal, but he'd gotten a pile of Teigu and Shingu.

The Overlord world lacked high-tier gods who controlled the rules—but the YGGDRASIL game clearly had admin-level authorities.

"Hey? Hello? System, you there?"

Setsuna finally called on his Dimensional Civilization System again.

"After I declare war on the Overlord world, is there a world authority I can claim?"

"..."

[World scan in progress...]

The system paused briefly.

Then responded in a mechanical tone:

[The Overlord world does not contain high-tier gods, but upon victory in the war, you may claim control over the YGGDRASIL game.]

"Game control?"

Setsuna blinked.

"So I'd basically be a game player like the Sorcerer King? I could create characters? Rebuild the Great Tomb?"

[Affirmative. You may consume resources to create anything within YGGDRASIL.]

The system answered.

Setsuna understood.

The Sorcerer King's abilities were treated as a world authority. He could use Nazarick's resources to create characters and customize NPC data.

After claiming this authority, Setsuna could do the same.

"Well, that makes it simple."

He cleared his throat.

"No need to hold back. Wipe them out completely."

"After the war ends, I'll recreate them from scratch. I'll be their only creator and rebuild Nazarick under my name."

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