Crossover Shipgirls: Building a Dimensional Empire from Scratch

Over the course of several days, the girls brought back from the Previous Era gradually settled down within the Starsea Empire.

MEI, Mobius, Vill-V, and the other scientists devoted themselves diligently to study and research, doing their best to quickly catch up with the Empire’s level of advancement before independently beginning their own projects.

Eden and Elysia were busy familiarizing themselves with life in the Starsea Empire, wandering aimlessly through the capital every day. Sometimes they would even take a spaceship out into outer space just to look around.

Pardofelis was directly sent to school for further education.

She was the youngest at the moment. Back on Dusk Street, she could only survive by stealing. The Starsea Empire had no need for her to be a chivalrous thief, nor did it require anyone to rob the rich to help the poor. Naturally, the best option was to let her attend school first.

Everyone from the Previous Era was quite satisfied with their new life in the Starsea Empire.

Under Sophon’s leadership, the Angeloids carried out another full campaign in the Honkai world, officially incorporating it into the territory of the Starsea Empire and rebuilding its administrative system.

The entire process flowed smoothly, requiring no extra effort from Setsuna.

With experience gained from more than a dozen previous worlds, it did not take long to establish this place as a fairly decent vassal state.

It seemed that the conquest of this world had now reached a perfect conclusion.

”Reporting to Commander. After comparative analysis between the Previous Era, the Current Era, and the timeline of Saga of the Shattered Swords, we have recruited all companions who could be recruited.”

Sophon reported in her cool, mechanical voice.

”In the next phase, after stabilizing the situation within the solar system, we will dispatch a deep-space expedition fleet to explore more distant regions of the universe.”

”Mm. Pay attention to any traces of civilized activity and approach cautiously.”

Setsuna thought for a moment.

”Also, if I remember correctly, there’s still a minor issue left regarding the strategy for the Previous Era?”

”Call Grey over. And bring the personnel who were previously in charge of Honkai energy research on the Honkai-01 Space Station as well.”

...

Inside the Imperial Valkyrie Academy.

After a full day of classes had ended.

”Haaah—”

Kiana, Raiden Mei, and Bronya returned to their dormitory one after another.

The white-haired girl threw herself onto the bed.

”I’m so tired, so tired!!—”

”Ahhh, the exams here are way too hard!!! They’re five times harder than St. Freya’s—no, ten times!!”

Kiana muttered with her face buried in the pillow.

At St. Freya, she could barely scrape by relying on talent alone. But at the Imperial Valkyrie Academy, all courses were aligned with the interstellar era.

Aside from Valkyrie combat training, there were subjects like quantum mechanics, celestial mechanics, high-energy physics, and more—enough to make their heads spin.

The difficulty was on an entirely different level compared to previous subjects like history, geography, and biology. The teachers were all temporarily transferred from the Research Division.

”Bronya, teach me.”

The white-haired girl pushed her tablet toward Bronya.

”I didn’t understand today’s physics class again. Help me, please.”

”...”

Bronya remained expressionless, clearly prepared for this.

”Kiana is actually taking the initiative to study. How strange...”

”You are the Commander’s daughter. Graduating from the Imperial Valkyrie Academy shouldn’t be difficult, right? As long as Commander says a word to Theresa or Instructor Himeko, that would be enough.”

”That’s different!”

Kiana puffed out her cheeks.

”I’m going to rely on myself to become the strongest Valkyrie. And then, and then...”

”Mm... Commander promised me something. I have to accomplish it!”

”?”

Bronya had no idea that Kiana was preparing to compete with Cecilia for the Commander.

She sat up on the bed and began tutoring Kiana.

”By the way, Commander went to the Honkai world again and brought back a lot of people.”

Durandal scrolled through her phone while casually joining the conversation.

”They’re from fifty thousand years ago—the Fire Moth of the Previous Era. Several of them are extremely capable scientists. The Divine Keys we use later were created by them, and the MANTIS surgeries are also related to them.”

”There was even a Herrscher, right? I think she’s called the Herrscher of Origin? The pink-haired older sister who came to visit the academy before.”

”Oh—”

Raiden Mei nodded.

”I’ve read about them in the history books. They’re incredible.”

”I hope I’ll have the chance to fight alongside them in the future.”

”I remember hearing that the history over there was changed as well?”

Bronya suddenly spoke up.

”Altering the world fifty thousand years ago would cause a severe butterfly effect.”

”From now on, human civilization has never gone extinct. It has continued uninterrupted since the Previous Era.”

”Um, Bronya would like to ask—do our history textbooks need to be replaced?”

Originally, the history books contained fixed facts. But now she subtly realized that with time-travel technology, not only the future—even history itself could be arbitrarily reshaped.

”I hope the final exams will still be based on the history we studied. Otherwise, we’ll have to memorize a lot more key points...”

Raiden Mei sighed and organized her textbooks and materials.

As an honor student, although she had initially been startled by the advanced subjects in the Starsea Empire and nearly failed to keep up,

Fortunately, after a period of hard work, her grades once again ranked among the top.

She felt a small sense of pride.

”The day after tomorrow is the weekend. Where should we go?...”

”Maybe visit the lunar research base? It requires advance reservation, right?”

Mei felt that life in the Starsea Empire was extremely fulfilling.

It was interesting and enriching. She had met companions from various worlds and learned all kinds of advanced knowledge. It was far happier than her previous life at St. Freya.

As she thought about it,

She considered taking some time to visit the Honkai world to see what it looked like now.

”?”

”Wait!”

Raiden Mei froze, suddenly realizing a massive BUG.

The worldline had been altered.

In the past, she had been the young lady of ME Corp. Since Cocolia had been taken away by Setsuna at an early stage, naturally the false accusation and imprisonment of Raiden Ryoma had never occurred.

Because of her connections, ME Corp had also managed to fare reasonably well after Earth became a vassal state.

While in the Starsea Empire, she would occasionally keep in touch with her family.

But now, the Previous Era—which had originally been destroyed—had survived and continued from fifty thousand years ago until the present. The Current Era would never come into existence.

If the Current Era did not exist, then ME Corp did not exist. The reason she herself had not disappeared was probably because she had become entangled in causality with the Starsea Empire.

”Ah???”

Raiden Mei and several other girls in the Imperial Valkyrie Academy simultaneously voiced the same soul-deep question:

”Where’s my dad? Where’s my mom? Where’s my family?!”

”Commander, save me!!”

...

Half an hour later.

Raiden Mei, Bronya, and a group of girls from the Imperial Valkyrie Academy hurried into the administrative center.

”Commander, we have a problem!!!”

Raiden Mei was out of breath from running, not even bothering with prior communication or an appointment.

In truth, this wasn’t something that could be explained in just a few sentences over a call.

”The history of the Honkai world was changed, so th-then... what are we supposed to do from now on?”

”The Current Era has disappeared. ME Corp is gone too. My family—and everyone on Earth—have they all been erased?...”

Mei struggled to catch her breath.

”Um, Bronya just tried contacting that world and found that all the numbers were invalid. Communication is completely cut off.”

Bronya held up her phone.

”They... seem to be gone.”

Durandal, Shigure Kira, and the others had discovered similar issues.

Although they had been living in the Starsea Empire, many of their parents and family members were still in that world.

Under Sophon’s management, the vassal state had previously been running in perfect order. They would check in with each other from time to time and even visit when they had the chance.

But after the Previous Era overwrote the Current Era, communication was suddenly severed. In the new timeline, their families had never appeared at all.

Even if they boarded a spaceship now and passed through a transmission anchor point, they would only find the bustling world of the Previous Era—completely unrelated to the Honkai world they remembered.

”Eh? Like this?...”

Elysia instantly understood the situation and stared blankly at Setsuna.

”Commander, in order to save us, did you make the people of the original world disappear?”

”I... I’m very grateful that you crossed fifty thousand years to save humanity here. But if it came at the cost of another human civilization, then that... that isn’t right.”

If her own survival from the Previous Era to the present had come at the cost of the Current Era, she would rather have followed the original worldline and perished together with the Previous Era.

At the very least, knowing that humanity had ultimately defeated the Honkai would have been enough.

”So in other words, I should have properly died fifty thousand years ago?”

Eden thought for a moment.

”Pretend we never met, never came here, and let everything return to its proper track?”

”It doesn’t really matter to me. That was my original ending anyway.”

”Stop, stop, stop. Commander didn’t bring you back just to have you stage a tragic drama here.”

Grey raised her hand to halt Eden’s spiraling thoughts.

She then looked at the anxious Raiden Mei.

”Calm down. There’s no need to panic. This situation is within our contingency plans.”

”Though handling it will take a little time.”

”Hm?”

Mei realized that Setsuna did not seem particularly surprised.

”Commander, you anticipated this?”

”Of course. Your reaction was a bit faster than I expected. I just called the researchers over, and you all arrived immediately.”

Setsuna smiled.

Inside the administrative center, the research lolis who had previously worked on the Honkai-01 Space Station, along with Tesla, Planck, Einstein, and other scientists from the Current Era, had already gathered.

”You explain it to them.”

Setsuna gestured toward Grey.

She guided Mei, Bronya, and the others to take their seats.

”From the observational perspective of this universe, the Current Era has indeed been erased. But that does not mean that world and your families have been annihilated.”

Swish—

A bizarre image was projected onto the holographic interface before them.

It resembled a world formed of blue quantum layers, stacked upon one another, with strange and fantastical scenes flickering within.

”?”

”...The Sea of Quanta?”

Bronya vaguely recognized it. It had been mentioned in textbooks, though not studied in depth at the academy.

She only knew some of the basic concepts.

”Smart. Have you considered joining the Research Division in the future? I think you’ve got potential.”

Grey rubbed Bronya’s head.

”When we conquered the Current Era, we handed over its entire administrative management to Sophon.”

”Each Sophon can connect with the others and upload data to the Starsea Empire’s primary control unit—Sophon No.1.”

”Strangely enough, even after the Previous Era replaced the existence of the Current Era, Sophon No.26—originally assigned there—remained connected.”

The nanorobot snapped her fingers.

Beside them, Sophon—dressed in formal attire and wearing her usual cool expression—immediately projected a communication interface.

”Sophon No.26, report the situation.”

”...Acknowledged.”

”Sophon No.26 is currently conducting administrative management within the Honkai universe.”

Another Sophon, identical in appearance, appeared on the screen.

”All conditions within the solar system are normal. Construction progress on Earth for the previous quarter is as follows: one small-scale starship assembly plant completed, seven space transport vessels assembled...”

A vast amount of data streamed back in synchronization.

”Thirty-two standard hours ago, this universe observed a suspected change in cosmic structure. However, my computational capacity was insufficient to deduce what occurred.”

”Additionally, the transmission anchor previously used to connect to the main universe has disappeared. This universe has lost physical linkage with the Starsea Empire’s core territory. Transport fleets are currently blocked. Requesting redeployment of a transmission anchor.”

”???”

Hearing the Sophon connected to the Current Era, Raiden Mei was overwhelmed with emotion and hurried to the holographic interface.

”Miss Sophon! Miss Sophon!”

”Please—are my family members safe?”

”...”

The Sophon on the other side seemed puzzled. After briefly closing her eyes to conduct observation, she responded.

”If you are referring to Raiden Ryoma, his vital signs are stable. He is currently handling corporate affairs within ME Corp.”

”By biological standards: alive.”

”What about Bronya’s family?”

”Alexei Sydavich Zaitsev. Currently residing in Siberia.”

”M-me, me, what about me?...”

A group of girls crowded around Sophon, bombarding her with questions.

In the past, they had felt a certain reverence toward this cold artificial intelligence. Now, she seemed incomparably reassuring.

After receiving confirmation that their families were safe and that nothing there appeared to have changed, everyone let out a collective sigh of relief.

”Haaah—That scared me... I thought they had all disappeared.”

Raiden Mei patted her chest, finally calming down.

But then they fell into even deeper confusion.

”Then... what exactly is going on?!”

The Current Era—and the Sophon managing it—still existed and could communicate with them.

Aside from the transmission anchor connection being severed, no abnormalities had been detected.

But where was that Earth now?!

Raiden Mei, Bronya, and the others exchanged glances before finally casting pleading looks toward the researchers.

”In another parallel world. Or perhaps within a bubble world.”

Tesla spoke quietly.

”You’ve all learned at least a little about the Tree and Sea before, haven’t you?”

”If we compare the entire universe to a great tree, it is the birthplace of all truths and laws. Upon its branches are nurtured countless worlds beyond measure.”

”Each branch represents a form in which a civilization exists. Each flower and leaf is the present and the past they leave behind along the dimension of time.”

She slipped into a scientist’s habitual mode, giving the young Valkyries an impromptu lecture.

”The Imaginary Tree is like a server that records game data. A server called the Imaginary Tree can take a save file from any point in any game and generate a new, parallel world from it.”

”On this special existence known as the Imaginary Tree, time moving strictly forward is not an absolute fundamental law. It possesses the ability to cut from spacetime and create entirely new worlds...”

”Huh?...”

Kiana had come to help, but the moment Tesla began explaining the Tree and Sea theoretical framework, it all turned into incomprehensible scripture to her.

”Commander, I can’t understand any of this!!!—”

The white-haired girl squeezed next to Setsuna.

”Can you translate?”

”Even a paramecium could understand this theory.”

Bronya remained expressionless, listening with great interest and nodding repeatedly.

”So the Current Era is currently living within a parallel world on the Imaginary Tree?”

”Correct.”

Tesla nodded.

”When Commander altered history, from the perspective of this universe’s observation, the Previous Era completely overwrote the Current Era. Pay attention to the qualifier—within this universe.”

”But from the standpoint of the Imaginary Tree, forcibly distorting spacetime with external power is equivalent to squeezing it off one branch and onto another—essentially pushing it from one parallel world into another.”

”Uh... of course, it could also have fallen into a bubble world within the Sea of Quanta.”

”Ohhh...”

Although they did not fully understand, knowing that the world still existed helped everyone calm down considerably.

”Then is there still a possibility for us to go there?”

”The transmission anchor disappeared... Entering the Imaginary Tree or the Sea of Quanta sounds extremely complicated, right?”

”No. It’s merely a parallel universe within the Tree and Sea.”

Grey waved a finger.

”We have at least two ways to get there.”

”First, Commander can use the power of the Herrscher of the Void to open a passage into the Tree and Sea. But if Commander has to personally act every single time, that would be too troublesome.”

”Second, there’s a more interesting method.”

”As early as the era of Saga of the Shattered Swords, we had already planned to conduct exploratory work on parallel worlds and bubble worlds within the Tree and Sea.”

”We even made a special trip to acquire a vehicle specifically designed for travel within the Tree and Sea.”

”Oh? You weren’t even born back then? No matter. We were already planning to explore the Tree and Sea anyway—bringing you along for a little trip would work just fine.”

”???”

Everyone froze for a moment before suddenly realizing what she meant.

The object she referred to was the one originally designed by Vill-V and constructed by Fire Moth in the original worldline—a Divine Key capable of controlling space and opening passages to the Sea of Quanta.

—Cosmic Juggernaut.