Crossover Shipgirls: Building a Dimensional Empire from Scratch

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As Setsuna and Richelieu once again stepped into the Grand Library, the once sparse dome-shaped building had now amassed an impressive collection of books.

Rows upon rows of bookshelves were neatly organized by world classification, with countless volumes meticulously arranged.

Looking up, the shelves were clearly labeled: Azur Lane Series, Siren Series, Gundam Series, Type-Moon Series, and more. Each category occupied one or several shelves according to the volume of knowledge available.

In the side halls, there were also numerous books purchased from the Miss Kobayashi’s Dragon Maid and Date A Live worlds, covering everything from cutting-edge science and technology to literary classics.

Setsuna had outright purchased several large-scale libraries from different worlds and transported their entire collections here, offering the base’s residents a variety of leisure activities.

Hundreds of shipgirls, Bulins, and Heroic Spirits were scattered throughout the library, either sitting or standing, each engrossed in their respective books.

Some Bulins were reading manga, while others were diving into advanced technical manuals from other worlds.

”Buli! So this is how lithography machines are made, buli! I got it! Should we try building a few computers or gaming consoles to play?!”

”Xbox? PS5? If we make them, they’ll be way more powerful than those—let’s just call it PS20! But... making games is tough.”

”Does anyone here know how to develop games?”

A purple Bulin exclaimed in awe, only to be immediately whacked on the head by a golden Bulin standing beside her.

”Keep it down! This is a library, you idiot!”

Meanwhile, Nero was seated at a table with two different world history books spread out before her. She compared them carefully, then poked Gudako sitting next to her.

”I think their records of me are incorrect. I was not a tyrant! And I never burned Rome!”

”That’s another world’s Nero, it has nothing to do with you...” Gudako replied without looking up, pushing a magic book towards Nero.

”Hey, do you know this spell? If you do, teach me. If not, I’ll go ask that big dragon lady instead.”

”My class is Saber. Besides, this isn’t even a Chaldea magic book...”

”...”

”Looks like Lucoa has been managing things quite well,” Richelieu whispered to Setsuna.

”Indeed...” Setsuna nodded in agreement.

Ever since he handed over the management of the Grand Library to Lucoa, he hadn’t needed to intervene.

Not only had she meticulously organized the existing books, but she had also authored a considerable number of magic books, making them readily available for reference.

With her identity as Quetzalcoatl, she was the perfect fit for the role of the wise guardian of the Grand Library.

The two continued forward, passing through the main hall and several side halls before arriving in front of Lucoa.

She was still dressed in her usual attire—short shorts and a T-shirt—while placing her enormous ”sins” on the table in front of her, eyes closed in a relaxed manner as she guided the nun-dressed Nia Honjo.

”Nia, no, you can’t do that,” Lucoa advised gently. ”When using the Future Entry function of Rasiel, your descriptions must be precise... And the target of interference cannot be too powerful…”

”Running into the Commander at an empty beach tomorrow? That’s impossible to achieve…”

”There are simply too many people you’d need to influence—so many shipgirls and Sirens patrol the port daily. You can’t possibly interfere with all their futures at the same time...”

On the table in front of them lay the massive tome of Rasiel.

Nia Honjo, holding a pen in one hand and resting her chin in the other, looked like a student deep in thought.

”Eh? That won’t work? Then can I try a smaller location? Like running into him at a park or a restaurant?”

”No good either?! Am I too weak…? Ugh…”

”Eh?!”

Upon noticing Setsuna approaching, Nia hurriedly stowed away Rasiel and dispelled her Astral Dress.

She reverted to her casual clothing, her cheeks flushed as she shyly greeted him.

”Morning, Setsuna.”

”It’s already noon…” Richelieu sighed, rubbing her temples.

Who knew why this Spirit, who had been ”abducted” into their ranks, had such a sudden change in attitude?

Perhaps she found being a Spirit and living in this world rather enjoyable?

After all, she was still an innocent girl—unlike the 23-year-old ”auntie” version of her from the original timeline.

She even had a hint of bashfulness to her now.

”Hey? You looking for me?”

”Got any new books from other worlds I can read?” Lucoa tilted her head and asked.

”I have a magic book I can’t understand. Thought you could help.”

Setsuna handed the recently acquired skill book to the dragon girl before him.

”Hm?”

Lucoa’s interest was piqued, and she opened her eyes to reveal a pair of striking yellow-green heterochromatic pupils.

”Hiding one’s presence and blending into the world itself… I do know a similar spell,” she remarked.

”But being able to conceal oneself from everyone... hmm, that’s quite remarkable.”

”Where did you get this from? Never mind, it’s definitely from another world—forget I asked…”

After reading through the book for a while, Lucoa finally looked up.

”This isn’t just your typical stealth magic—it’s more like a cognitive interference spell applied to oneself.”

”Huh?” Setsuna was a little surprised, realizing he hadn’t fully understood it before.

”Under the effect of this spell, most of your actions will appear ’reasonable’ to others. As long as you don’t go around slapping people in the face, they won’t notice your presence.”

”Hm… ah… I don’t quite know how to explain it properly. In short, it’s not particularly effective against normal people, similar to Tohru’s perception-obscuring spells. However, it’s exceptionally potent against gods.”

Lucoa scratched her head, looking uncharacteristically troubled.

Even with her vast experience, Lucoa could tell that the reward provided by the system was of a significantly higher tier—something she had never encountered before.

”So it’s essentially an anti-god skill?”

Setsuna had initially thought of it as an enhanced version of an Assassin’s stealth ability. However, it appeared to be the ultimate plus version of a cognitive interference spell.

Tohru, Kanna, and Lucoa frequently roamed human society and often reverted to their true dragon forms.

Yet, even with horns on their heads, tails trailing behind them, and the ability to soar through the skies, no human ever found their existence odd.

This was the result of cognitive interference magic. From the perspective of ordinary people, there were no dragons or dragon girls—Tohru was simply a girl with blonde twin-tails.

This spell functioned in a similar way.

For example, if there was a god in a medieval-style world observing the realm from a higher-dimensional space, and Setsuna and his shipgirls showed up in spaceships to bombard the land, their drastically different style from the locals would surely attract the god’s attention, potentially provoking it to intervene.

However, under the effects of the spell, as long as they didn’t blow up an entire planet, Setsuna’s actions would fail to register in the god’s perception—his presence blending seamlessly into the world’s background.

”Can you teach me?”

Setsuna was primarily concerned with the spell’s practical application.

”I can… You, Tohru, and that child named Mio should all be able to learn it.”

Lucoa pondered for a moment before answering.

”Wait, so does this spell work on you?”

Nia’s eyes sparkled with mischief.

”Me? Well, I suppose I do count as a goddess of sorts, so yes, it would work on me… Why do you ask?”

The dragon girl tilted her head in confusion.

”So if Setsuna uses this spell, and does some naughty things with you, it would still seem perfectly reasonable?”

Nia’s mind was once again flooded with inappropriate thoughts.

”He could sneak into your room at night while you remain unaware, thanks to the spell’s effects… You wouldn’t notice anything unusual…”

”You’d just feel your body getting hotter, and more eager… and then…”

”With a special kind of power, he could do all sorts of things to the high and mighty goddess without her realizing it, slowly leading her down the path of corruption…”

As she spoke, Nia became more and more excited, pulling out a sketchpad and scribbling furiously.

”...?”

Lucoa blinked in bewilderment, turning to Setsuna.

”Eh? Is that what you had in mind?”

Thump!

Setsuna swiftly delivered a chop to Nia’s head.

”I put you under Lucoa’s care so you could study properly—not so you could draw erotic doujins, got it?!”

...

Bang!

After being tossed into a small dark room by the dragon lady, Nia was effectively placed in time-out.

Lucoa then invited Setsuna and Richelieu to sit down. She took a stack of drafts from the bookshelf and pushed them toward Setsuna.

”Commander, there’s something else I’m quite interested in.”

”What do you think about the concept of Inverse Form?”

”Why are you bringing this up?”

Setsuna was momentarily taken aback.

In the Date A Live world, Spirits undergo inversion when subjected to extreme external stimuli, causing their Spirit Crystals to reverse and their spiritual energy to enter negative values.

Once inverted, they go berserk, and their Angels transform into Demon Kings—essentially a kind of dark transformation.

”I was going through the DEM data you brought back and found that Westcott had some theories on this subject.”

”He’s a pureblood wizard, right? He proposed absorbing a Spirit’s Inverse Form to acquire the power of the demons.”

”That bastard’s research? Yeah, I know about it.”

Setsuna recalled that since he had intervened early, Westcott was still just a rookie with no demon under his control—Kurumi alone could take him down.

”If Angels and Demon Kings exist in a one-to-one relationship, that means each Spirit should theoretically have an Inverse Form...”

”I think we should study the relationship between Angels and Demon Kings and attempt to separate the demon entities.”

”That way, Spirits could control their inverse power at will, effectively gaining an additional combat form.”

Lucoa explained further.

”?!”

Setsuna was astonished.

In the original story, Westcott aimed to induce inversion in Spirits and then steal their Spirit Crystals to harness the power of their Demon Kings.

But what Lucoa was suggesting was entirely different—giving Spirits the ability to control their Inverse Form, treating it as an alternative transformation they could freely switch between.

Alright, fair enough. Westcott couldn’t hold a candle to Lucoa’s intellect.

”Can you really pull that off? That sounds insane...”

”I think it’s possible, but I’ll need more time to research it thoroughly… and I’ll probably need your help or the Spirits’ cooperation at some point.”

Lucoa mused, deep in thought.

”Besides, studying gods from different worlds is quite fun, don’t you think?”

”Sure, I’d love to see Spirits being able to transform freely...”

Setsuna considered it for a moment and then nodded.

”After all, Seijuro Yatogami is way cooler than regular Tohka.”

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