Crossover Shipgirls: Building a Dimensional Empire from Scratch

Setsuna and the shipgirls were surprised, and even the Zero-Homer was a little taken aback.

”Sorry, I thought that as ’gods’ on the technical level, you should have already mastered mathematical laws.”

”Otherwise, how did you achieve such accomplishments?…”

Faster-than-light travel.

Even to a native god-tier civilization like the Zero-Homers, it was something that could only be called ’divine.’

For gods to not have mastered certain knowledge was strange.

”…”

”Our focus of development was different.”

Setsuna coughed lightly, speaking tactfully.

Most of the Starsea Empire’s technology came from Stellaris and the Azur Lane worlds.

All of it was for fighting.

In truth, it was very practical. If you were stronger than others, they would calmly sit down and reason with you.

Because you had both the freedom to negotiate, and the freedom to flip the table.

”…Is that so?”

The Zero-Homer thought for a moment, saw that Setsuna had no hostility, and that everyone was curious.

So he simply began to explain.

”You’ve seen weapons that manipulate universal laws, right? There are many two-dimensional spaces nearby that were struck by dual-vector foils.”

Everyone nodded.

”Then what do you think about manipulating mathematical laws, or using them as weapons?”

”…”

Yukikaze thought for a while.

”Make 1+1=3? Then all of the enemy’s fundamental sciences collapse?…”

”No.”

Kayo Senju and several research lolis immediately shook their heads.

”Mathematics is a formalized tool. It has no meaning by itself. It belongs to logic, not science.”

”Changing mathematical definitions has no effect on reality. Making 1+1=3 is a logical contradiction, not a change in mathematical law.”

Saying this, one of the little lolis gave an example, pulling two apples from her pocket.

”One apple plus one apple equals two apples, right? Even if you define 1+1=3, in reality there are still two apples here.”

”If it were truly by modifying the laws that one apple plus one apple became three apples, then what’s broken is the laws of matter and conservation of mass-energy. It has nothing to do with mathematics.”

The research loli explained as simply as she could. Setsuna and the shipgirls pondered for a while, barely understanding the concept.

”Yes. Mathematics is an abstract concept. It does not directly act on reality.”

The Zero-Homer slowly nodded.

”When mathematical laws are mastered to the extreme, it means eliminating probability. All things in the world can be solved.”

”Perfect calculation of all events?!”

Kayo Senju and Grey froze for a moment.

Suddenly they thought of something unbelievable.

”Deduction and prediction of the future?! This really is a divine ability?!”

”?”

Seeing that several of the shipgirls were still confused, they explained further.

For a civilization with infinite mastery of mathematics, they could build a perfect mathematical model to calculate every complex system in the world.

From the current state, they could compute all future states. Every problem had a solution.

For example:

The butterfly effect is a chaotic phenomenon. A butterfly flapping its wings in South America could eventually cause a tornado in Texas.

Mastering mathematical laws meant being able to control every part of the chaotic model.

For example, making a butterfly flap its wings at the exact right moment and place to produce the exact desired result—such as causing a hurricane in South America.

”Causality?!”

Setsuna thought for a moment, and understood.

Using mathematical laws to clarify all causal relationships in the world, then guiding events toward the desired outcome.

Calling this a ’divine weapon’ was no exaggeration.

A somewhat extreme but fitting example: Ye Wenjie’s first broadcast to the universe could also be seen as a butterfly effect.

If someone wanted to quietly destroy humanity, the Trisolarans, and the entire galaxy, all they needed to do was push Ye Wenjie to act, and then wait 400 years for the result.

”Then… can you predict our future?”

Tai Yuan asked curiously.

”No, the main core cannot construct your mathematical model.”

”I suspect you do not belong to this universe. You come from a greater superstring cosmos or a higher-dimensional world. Otherwise, I would not have been captured.”

The Zero-Homer shook his head, and everyone’s expressions changed slightly.

That such an advanced civilization could deduce this far was remarkable. He was already very close to the truth, but Setsuna did not expose him.

”In short, after mastering mathematical laws, our civilization expanded at exponential speed. We quickly occupied an entire galactic cluster and annihilated all our enemies.”

”Because we possess deduction and the ability to foresee the future, a civilization that masters mathematical laws stands at the very peak of this universe. At the same time, wars between such civilizations are incredibly devastating.”

The Zero-Homer continued.

”Then, one day, we attempted to deduce the past and future of the universe. The result we obtained was unsettling.”

”Endless expansion, eventual heat death, or reduction to two dimensions, correct?”

Setsuna asked.

This too was the final outcome of the Trisolaran universe.

”Yes.”

The Zero-Homer nodded.

”The universe is dying. After deducing the universe’s future, we began our self-rescue.”

”Reducing the universe to zero dimensions, then rebooting it—that was the only method we could conceive to recreate the pastoral age.”

”Every civilization that mastered mathematical laws and foresaw the universe’s dark future joined us without exception.”

”…”

After listening to the Zero-Homer’s story, Setsuna fell silent.

He had originally thought the Zero-Homers were just performance artists. Now it seemed they were advanced civilizations making a final effort to save the universe after foreseeing its doom.

They could even disregard the survival of their own civilizations—because if the universe itself ceased to exist, nothing would remain.

”God from another world.”

”May I ask—when you look into the universe’s future, is it as dark as what we saw?”

The Zero-Homer raised his head and asked Setsuna, as if awaiting the final judgment.

”…”

Setsuna did not answer.

”Can you save this universe?”

The Zero-Homer asked again.

”?!”

”Hold on.”

Setsuna was stunned.

He had come to the Trisolaran universe only to scavenge useful technology and leave. What happened to this place was none of his business.

Even if the natives treated him as a god, saving the universe was hardly a task suited to the current Starsea Empire.

Perhaps they’d have to ask Rio Sonogami instead.

”Come on, since you know we aren’t a civilization of this universe, why would you ask us to save it?”

Grey looked at the Zero-Homer like he was an idiot.

”Because you come from a greater world. You are the only hope for this universe.”

The Zero-Homer paused, glancing around.

”I can offer you something of interest. You seem unfamiliar with certain law-based technologies of this universe.”

”Oh?”

Setsuna tilted his head slightly.

Even if the Trisolaran universe’s fundamental science lagged behind the Starsea Empire, it still had plenty of crooked but fascinating black technologies like dual-vector foils and sophons.

”But you will not obtain any guarantees from me. Let’s be clear: I will not share any technology, including faster-than-light.”

”I know.”

The Zero-Homer was unsurprised.

”And even if I didn’t bring it up, you would eventually find some other method to achieve your goals, would you not?”

”Smart!”

Grey gave him a thumbs up.

She wasn’t exactly a saint, inviting the Zero-Homer over just for tea.

If a native met an FTL god, they couldn’t possibly leave without offering tribute.

If the Zero-Homer tried to walk away, she would 100% track him to his homeworld and give them a taste of a Stellaris-style endgame crisis.

”Fine. I won’t promise I can do it in the future. Maybe when I’m bored, I’ll come here and run some experiments, try this universe rebooting thing.”

”And—I’ll let you live to go back.”

Setsuna answered.

He was indeed interested in seeing the Trisolaran world’s pastoral age.

Faced with a group of idealists determined to save the universe, there was no need to be too harsh. There might be opportunities for cooperation later.

”That is enough. Thank you.”

The Zero-Homer nodded slightly.

...

...

A few days later.

The Eternal Snowfall returned to the Solar System Starbase.

Inside the database, a heap of alien civilization data was added.

The Zero-Homer had truly hoped Setsuna would take up the responsibility of saving the world, and so shared with him various frontier theoretical technologies.

—Even if, in the eyes of the research lolis, most of it was just sub-light native backward toys.

There were still some interesting things, however, which the Sirens and research lolis pored over with enthusiasm.

On a bright morning—

Setsuna crossed off all the items on his memo.

”Zero-Homers, complete.”

”Pocket-universe creation technology, acquired, under study…”

”Mathematical laws, basic concepts grasped, deeper research pending…”

All of the objectives set before departure were completed. The spoils were too many to count, to be slowly digested later.

Shwoom—

He closed the holographic interface and connected to the fleet comms.

”Everyone, we’re going home!”

...

[Communication Node Established]

[Node 17: Trisolaris]

After spending a few days in the Trisolaran world handling follow-up tasks, the fleet began preparing for the return journey.

Some research lolis and Angeloids temporarily stayed behind at the Solar System Starbase of this universe.

They continued studying various law-based weapons in the Trisolaran universe, and also attempted to manufacture controllable dimensional-reduction strike weapons.

The various law-based weapons of the Trisolaran world, though unable to surpass lightspeed, were highly destructive and often had unpredictable consequences.

Until they could be fully stabilized, they were only suitable for experiments in this universe, lest any mishap occur in their main world.

The shipgirls cleared out a security zone of over 500 light-years around the Solar System Starbase.

In the surrounding star regions, they deployed FTL detection devices—any alien civilization daring to approach would trigger an early warning.

Even if some reckless civilization launched an attack, there would be at least 500 years of warning time—more than enough for the fleet to turn the attackers’ homeworld into a mining field.

After settling affairs in this universe—

Setsuna returned to the capital with the shipgirls.

Whumm—

The Eternal Snowfall passed through the void, descending above Earth.

It was midday. In the capital, little lolis, Heroic Spirits, and Spirits raised their heads to see a second sun in the sky.

The starship’s metallic hull reflected the dazzling sunlight. At such close range, it was even more brilliant than the star itself.

A cheer erupted across Constantinople.

Little lolis jumped and waved at the towering ship above.

The Spirits tidied their dresses, bathed, combed their hair, and changed into their prettiest clothes.

After so long apart, they had to show their best side before the Commander.

The Heroic Spirits didn’t care much for interstellar war, but they cared deeply for their Master. Even the Ahoge King, who had been eating at the buffet, dropped her bowl and chopsticks to rush out and welcome Setsuna.

No citizen of the Starsea Empire could mistake it—that was the Empire’s flagship.

The Eternal Snowfall’s return marked yet another triumphant expedition of their Commander.

Unlike the natives of other worlds, the sight of a starship blotting out the sky did not inspire fear. Instead, it brought them peace of mind.

Clunk—

After the Juggernaut slowly entered Earth’s orbit, a smaller starship carrying the crew descended into the atmosphere.

Normally, the Eternal Snowfall remained in space as Earth’s second satellite.

In theory, they could put it away, but since retrieving and deploying it each time would be troublesome, they simply activated its anti-gravity mode and left it hanging in orbit.

On occasion, curious lolis could even go aboard for a tour.

”Husband, it’s been so long.”

”Commander, welcome home.”

”Master, you came back alive… I’m so glad.”

As soon as the hatch opened, Mio and Tohru rushed forward.

One to the left, one to the right, they fully occupied his arms.

Jeanne Alter, meanwhile, looked awkward and sulky.

”Tch, why did it take you so long this time? Didn’t you say flattening those Trisolarans would only take a moment?”

”I waited forever at the base. Hmph, I should’ve gone with you.”

”Exactly!”

One of the Spirits puffed her cheeks, gazing up at Setsuna from his embrace like she was throwing a little tantrum.

”I thought it would only take a week or two, but you were gone over two months. I was worried sick.”

”Hey, I wasn’t out of contact. You called me every few days. What was there to worry about?!”

Setsuna laughed, pinching Mio’s cheek.

Looking up, he saw the little lolis, Spirits, and Heroic Spirits crowding around the ship, layers upon layers.

After dealing with so many Trisolaran pests and alien vermin, these familiar faces looked especially pleasing.

”Besides, this trip wasn’t just about dealing with the Trisolarans. We also eliminated the Singer, and even made contact with the god-level civilization of the Trisolaran universe—the Zero-Homers.”

”The harvest was great. Oh, and we also picked up a side mission: saving the universe.”

”Hm?”

Tohru tilted her head, confused.

”Are we supposed to save some planet in dire straits?”

”No, the whole universe. An entire cosmos. Someone asked me to reboot the Trisolaran universe one day.”

”Hah?!”

...

A little later, after the Spirits, Heroic Spirits, and others stationed here had clung to him for a while, everyone returned to the administrative center.

The shipgirls wore looks of lingering excitement, still savoring the thrill of using FTL technology to thrash alien natives.

They almost wished the Commander had come back later, so they could enjoy interstellar war to their hearts’ content.

The Heroic Spirits, Spirits, and other stationed members, meanwhile, were full of curiosity.

The technology of scientific worlds had little to do with them as magic-side beings, but they listened as though to an epic tale.

”Let me tell you, our Northern Union comrades destroyed six alien star systems! And—get this—we even ran into alien mega-corporations.”

”Mega-corporations, you know, those super-capitalists of the interstellar age. The Soviets strung them all up on lampposts. Meeting our Northern Union was just their bad luck, haha…”

A cute purple-haired Northern Union destroyer shipgirl excitedly recounted her glorious exploits to the stationed companions, leaving them all wide-eyed with wonder.

”Ahem. So, that’s the rough outline of what happened in the Trisolaran world.”

Setsuna opened the holographic interface and, with the projection, narrated the fleet’s journey in the Trisolaran universe.

From their first descent, coincidentally running into the United Human Fleet and the droplets.

To their impromptu Spring Festival celebration of two thousand blasts, using the Fallen Star Lance to wipe out the Trisolarans and conquer Earth.

To their encounter with the Singer, seizing dual-vector foils and photoids.

Finally, through a pair of rather absurd methods, finding the Zero-Homers, and after exchanging words with them, receiving the outrageous mission of rebooting a universe.

The Spirits and dragon girls propped their heads in their hands, as though listening to a grand science fiction epic.

Each marveled at the vastness and darkness of the Trisolaran universe.

In that place, low-level civilizations shivered under the Dark Forest law, hiding themselves just to survive.

Stronger civilizations, like the Singer, in pursuit of more living space, began systematically cleansing and exterminating lesser civilizations.

They even attempted two-dimensionalization, hoping to survive amidst the universe’s dimensional collapse.

And then there were the god-tier civilizations like the Zero-Homers, running themselves ragged for the future of the universe.

From the laws of mathematics, they had deduced the universe’s bleak destiny.

In order to save it, they placed their faith in a civilization from another world.

Setsuna’s narration lasted for several hours, and everyone listened with rapt attention.

”Ooh…”

”The Trisolaran natives are so annoying.”

That was the unanimous first conclusion of the Spirits and Heroic Spirits.

”And the Singer—utterly heinous.”

Next, when they heard about mathematical law weapons, Lucoa opened her squinted eyes slightly in surprise.

”Causality, hm…”

”As expected, whether technology-side or magic-side, in the end all paths lead to the same place.”

In magical worlds, many beings known as ”gods” possessed terrifying authority to reverse cause and effect.

...

God-tier scientific civilizations could achieve the same.

With just a fragment of data, they could deduce the fate of the universe billions of years ahead.

By constructing mathematical models of cosmic operation, they could guide the development of all things toward their will.

A civilization that mastered mathematical laws could glance once and calculate with absolute precision the rise and fall of a lesser race across hundreds of millions of years.

To natives, they truly were indistinguishable from gods.

”It’s a pity we didn’t find the Zero-Homers’ homeworld… I was hoping for a fight.”

Fu Shun leaned in curiously.

”A civilization of pure energy! What would their homeworld even look like? I really want to know…”

”Not necessary.”

Setsuna ruffled her hair.

”The Zero-Homers bear us no hostility, and even provided us with a mountain of data. There’s no need to raid their home.”

”In fact, when we run experiments in the Trisolaran universe, we may even have chances to cooperate.”

The Zero-Homer individual that Grey had caught was very clever—fitting for a god-tier civilization of the Trisolaran universe.

From the beginning, he understood the difference in power and never once harbored hostile thoughts toward the Starsea Empire, nor did he act foolishly.

Learning that the Empire’s tech tree was rather skewed, he proactively shared some research results.

Their goal was simple—rely on the Starsea Empire, this higher civilization from another world, to reboot the universe.

The Zero-Homers didn’t care about gains or losses between civilizations. They only wanted to reset the universe, to return to the pastoral age.

Setsuna was very interested in seeing whether they could succeed. In research of universal laws, the Zero-Homers had clearly gone further than the Starsea Empire.

Even if they were still lightspeed natives, with military strength far beneath his own, their strengths were still worth learning from.

If the mastery of universal laws could be combined with faster-than-light technology…

Both the Sirens and the research lolis felt their hearts race with excitement.

—

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