Crossover Shipgirls: Building a Dimensional Empire from Scratch

On the holographic interface, two massive Transformers were completely stunned.

It took them a moment to process what was happening.

”Starsea... Empire?”

”Ah! Right! I remember now! You said that once you built a faster-than-light ship, you’d send us back to Cybertron?”

”That fast?!”

Bumblebee shoved his head closer, curiously staring at the avatars of Setsuna and Grey on the other side.

After the Autobots and Decepticons had barely achieved a reconciliation, Setsuna had taken the Allspark and the Transwarp Key back to the Starsea Empire.

He had promised that one day he would send them home—and save Cybertron from its crisis.

”Fast?...”

The shipgirls were full of question marks.

After thinking about it, the Autobots’ concept of time was probably completely different from theirs.

For developing faster-than-light starships, with humanity’s conventional research standards, it would take who knew how many centuries.

The Transformers were clearly using Earth humans as their reference point when estimating the Starsea Empire’s efficiency.

”This time, we’re not just sending you home. We’re also taking care of Unicron while we’re at it.”

”Are you still at Sector Seven? Gather everyone. We’ll talk details after we arrive.”

Setsuna asked.

”Oooook!!!—”

Bumblebee dragged out the last syllable and sent a message to every Autobot on Earth.

”Hey, brothers! Someone’s coming to take us home!”

”Assemble!!”

Whoosh—

In an instant, across the world, vehicles and aircraft of all shapes sped toward Colorado.

It wasn’t uncommon to see cars erupt with blazing exhaust from the ground and take off vertically like aircraft.

All of them had been upgraded by Setsuna before. In human cities, waves of astonished exclamations rang out.

Before long.

Western White Eagle, Colorado, Sector Seven.

This had once been the facility used to research the Allspark. After Setsuna conquered the entire world and made Earth a vassal of the Starsea Empire, it had been designated as autonomous territory for the Transformers.

Beep—

Vehicles of all sizes arrived from every direction, smoothly transforming into their robotic forms.

Not only were there Autobots led by Optimus Prime—Bumblebee, Mirage, Arcee, and the others—but Megatron’s Decepticon forces were present as well.

”Boss? We can go home now?”

A gigantic combiner formed from five construction vehicles looked up at the sky.

”Earth’s actually not bad. If only the humans here would listen to our commands, it’d be even better.”

”...”

Optimus Prime shot Devastator a glance. A Decepticon was still a Decepticon. If Setsuna hadn’t upgraded his weapons and equipment—allowing him to defeat Megatron single-handedly—who knew what trouble they might have caused.

”By the way, I remember when we last saw that ship, it was this—big. I think it was called the Eternal Snowfall?”

Bumblebee scratched his head, flying around in circles in midair.

”I wonder what it looks like now?”

”Hoh...”

The Transformers had been deeply impressed by that Titan-class starship. It had been able to overwhelm the entire Autobot army without effort.

Its only weakness had been its relatively slow speed.

”...”

Megatron said nothing. Setsuna’s power far surpassed the Decepticons. He had clashed with him in humanoid form, Gundam form, and starship form.

In terms of technology, the other side held absolute superiority.

Crack—

Before long.

A deep rumble echoed through the sky.

”They’re here!”

The Autobots straightened, feeling a suffocating pressure descending from the heavens.

When they looked up again—

The majestic fleet of the Starsea Empire tore through space, gliding out from a teleportation anchor.

Compared to the battleships and cruisers they had seen before, these vessels were dozens, even hundreds of times larger.

Their designs were even more futuristic. The weapons mounted beneath and along their hulls were technologies the Transformers had never seen before.

Even by Cybertronian standards, these ships looked excessively advanced.

The dazzling sunlight was instantly eclipsed by the overwhelming fleet. A silent fear enveloped the human cities below.

”This is a routine patrol of the Imperial Fleet. All civilians may continue normal activities. There is no need to panic.”

Only after Sophon broadcast the announcement did humanity gradually calm down.

”Oh my God!!!—”

Bumblebee’s head spun in circles until he felt dizzy.

The spacecraft Cybertron once built were little more than toys compared to a fleet of this scale.

”Wait, these ships... are they the little girls who came with him before? Where is he?”

Mirage craned his neck, searching among the shipgirls for Setsuna.

At the far end of the sky, a colossal vessel could be seen splitting the horizon in two.

Due to its sheer size, it couldn’t land directly on the planet and instead hovered beyond orbit.

A smaller starship emerged from the docks of the Juggernaut and slowly descended to the ground.

”Everyone, Master is waiting for you. Please follow me.”

An Angeloid opened the hatch and gestured gracefully.

”???”

The Autobots were shocked.

”Huh?!”

”You’re saying—that one up there—is him?”

...

”Aba aba...”

A group of Autobots followed the Angeloid aboard the flagship of the Starsea Empire.

Among all the possibilities they had imagined for the Eternal Snowfall, they had never once considered that it would become such a gargantuan entity.

The bridge of the starship was extremely spacious. Even the massive Transformers could be accommodated with ease.

”Yo, long time no see?”

Setsuna greeted the Autobots with a smile.

”Whoa—”

Bumblebee stepped forward and bumped fists with him, scanning him up and down.

”Bro, you haven’t changed much, have you? So how did this thing get so huge?”

Pfft—

Setsuna laughed.

”A lot has happened in between. It’s not something I can explain in a sentence or two. If you’re interested, I can give you the short version later.”

”...It can take us to Cybertron now? This is what you developed using the Transwarp Key?”

Optimus Prime focused on the practical question.

”Of course.”

Shff—

Setsuna marked a location on the holographic star map.

Cybertron was roughly four light-years from Earth. For the current Eternal Snowfall, it was a destination that could be reached in an instant.

”On this trip, there are three things I intend to do.”

”First, send you home. Second, save Cybertron. Third, deal with Unicron.”

”Hold tight.”

Rumble!!—

Before the Autobots could react.

The starship skimmed past the orbits of the solar system at sublight speed and instantly activated its jump engine.

[Coordinates confirmed]

[Jump preparation: 5, 4, 3, 2, 1...]

Shff—

Bizarre, dazzling scenes flashed past the viewports, as if they had entered a temporal corridor.

”Whoa whoa whoa, is this light speed? Faster-than-light?!”

Bumblebee felt the disorienting distortion caused by warped gravity.

The Transwarp Key was merely a tool to open hyperspace corridors. Compared to jump technology capable of leaping across interstellar distances, it was far inferior.

The Decepticons were equally shaken.

In just two or three minutes.

With a faint tremor running through the hull, the starship arrived in a completely unfamiliar star system.

Alpha Centauri.

In the Three-Body world, it was the home of the Trisolarans. In the Transformers universe, it was the Autobots’ mother star.

A colossal metallic planet, roughly comparable in size to Saturn, slowly orbited its star.

Unlike any colonized world, the vast majority of Cybertron’s structure was composed of various metals.

The lifeforms born upon it were true silicon-based mechanical beings.

Magnificent mechanical megastructures rose across the planet like any intelligent machine civilization—futuristic and sharp.

Every design philosophy prioritized efficiency above all else. There was almost no unnecessary decoration.

Though Cybertron was grand, it carried a sense of desolation. Damaged buildings and barren wastelands exposed to the open environment could be seen everywhere.

Years of war had drained Cybertron’s resources. The Autobots had been forced to venture outward in search of new energy and habitable worlds.

”So fast!!—”

”How did you even do that?!...”

Optimus Prime and Bumblebee had only just been marveling at the miracle of jump technology when their attention was drawn to their homeland below.

After countless years of longing, they had finally returned to Cybertron.

For a moment, the Autobots were too overwhelmed to speak.

”It really is a bit desolate.”

Setsuna glanced downward.

The remaining Transformers on Cybertron stared in confusion at the fleet that had suddenly descended.

”Come on. I’ll help you rebuild Cybertron.”

Click—

The starship landed at Cybertron’s North Pole.

The native Transformers stared blankly at these visitors from another world.

In the countless years since their birth, they had never encountered carbon-based lifeforms voluntarily landing on Cybertron.

The climate here was not suitable for ordinary humans. Fortunately, Setsuna and the shipgirls could stroll unprotected through space without issue.

”Wow, so many robots!!—”

A group of little shipgirls hopped down, chattering as they curiously examined the surrounding Transformers.

”Tch. Not even close to my level... They can’t even transform into cute girls.”

The nanorobot developed a strange sense of superiority.

Just a bunch of tin cans—merely another form of intelligent machine civilization.

Boom!!—

When Optimus Prime and Megatron descended, it triggered an even greater commotion among the Transformers.

They had never imagined that after fighting to the death countless years ago, Autobots and Decepticons would return together aboard an alien starship.

Clank clank clank—

The remaining Transformers instantly split into two factions. One gathered behind Megatron, the other clustered around Optimus Prime.

Weapons unfolded one after another, dark muzzles aimed at each other.

In their understanding, the war had never ended. If Optimus Prime and Megatron appeared together, it could only mean a battle to the death.

”Stand down.”

Optimus Prime’s deep voice halted the unrest. Megatron also raised a hand, signaling the Decepticons to cease.

”What’s going on?!”

”These are... friends we met on Earth.”

After a brief pause, Optimus Prime swept his gaze across all the Transformers and spoke steadily.

”They have brought us back from Earth. We have decided to declare a truce with the Decepticons and work together to save Cybertron.”

His words were few, yet they stirred a tremendous uproar among the natives of Cybertron.

Megatron was even more succinct:

”Stand down. We’re not fighting right now.”

Having witnessed the Starsea Empire’s fleet, he knew that causing trouble now would be suicide. Moreover, he could no longer defeat Optimus Prime anyway.

”???”

All the Transformers looked uncertain, their gazes falling on Setsuna.

To earn recognition from both Autobots and Decepticons was unheard of.

”Mm... Long story short, we are a civilization from another world—the Starsea Empire.”

Setsuna cleared his throat.

”We previously borrowed the Transwarp Key. As promised, I will help you rebuild your homeland.”

”For the details, Optimus Prime and Megatron can fill you in.”

The development of faster-than-light technology had indeed depended on items obtained from the Transformers’ world. Naturally, Setsuna intended to help the Autobots in return.

Rebuilding an entire planet was not difficult for the Starsea Empire—especially for him now.

”Oh...”

Megatron and Optimus Prime briefly explained the situation on Earth.

They had left Cybertron in search of energy resources necessary for survival.

Now that a powerful civilization from another world was willing to solve the problem for them, no one objected.

”Brother, we use energon cubes to replenish our power. Unfortunately, the resources Cybertron can mine are getting scarcer.”

Bumblebee placed a large transparent cube before Setsuna, filled with a liquid-like fuel.

Setsuna and Grey dipped a finger into it. The AI immediately analyzed its data.

Refined from ores, crystals, and high-energy gaseous materials, then liquefied and compressed—this became energon.

Its energy level far exceeded that of Earth’s fuels. It was essentially the Transformers’ rations.

”Oh, so that’s the composition.”

Setsuna nodded and looked at Optimus Prime and Megatron.

”What does your ideal Cybertron look like?”

”Huh???”

The two leaders were caught off guard.

They had assumed Setsuna would take them to other star systems to gather resources and transport them back to rebuild Cybertron.

Why ask such a seemingly unrelated question?

After thinking for a moment, Optimus Prime spoke first.

”Long ago, Cybertron possessed countless resources. Metal covered the planet’s surface. Our factories and structures stood everywhere.”

”The North Pole was the central capital of the Federal Province—Kaon. It housed the largest smelting plant on Cybertron. Nearby were Iacon and Tarn...”

”The equatorial region contained the great proving grounds and the Sonic Canyon that stretched north to south. We often trained there. We also had computer microprocessor engineering facilities and institutes of computer science responsible for research. Sadly, due to resource shortages, they have long since fallen into ruin...”

He was completely immersed in memories of past glory, describing to Setsuna the golden age of Cybertron countless years ago.

”Sigh...”

Many Autobots listened with downcast expressions.

”That’s enough. Let’s focus on solving our current problems first. Cybertron’s energy supply isn’t even sufficient for us anymore.”

Megatron interrupted Optimus Prime’s reminiscence.

”Those Federal Provinces and buildings—do you have structural blueprints? The more detailed, the better.”

Setsuna asked again.

”Yes. Some were lost in the war, but I’ve recovered quite a few.”

Wheeljack stepped forward. One of the greatest scientists in Transformers history, he was not skilled in combat but excelled in maintenance and preserved vast amounts of data regarding Cybertron and the Autobots.

In a few swift motions, he transmitted the stored data to Setsuna.

With the Eternal Snowfall’s superior onboard AI analysis capabilities, Setsuna quickly grasped Cybertron’s structural design.

”Buddy, that’s a massive undertaking. You’re not planning to rebuild Cybertron from scratch, are you? That would take so much—”

Before Bumblebee could finish.

Clap—

Setsuna brought his hands together.

”Witness a miracle.”

Shff—

The authority of the Herrscher of Reason activated.

The entirety of Cybertron was instantly enveloped in a faint layer of Honkai energy.

Battle-scarred craters and uneven wastelands were filled and leveled in moments.

Magnificent megastructures and smelting factories that had existed only in historical records rose from the ground.

They were constructed out of nothing at a speed visible to the naked eye, completely disregarding any known physical laws.

Optimus Prime watched clearly. Many buildings were first shaped from thin air in their upper halves, suspended midair, before their lower sections and foundations were formed beneath them.

Stable, precise, flawless—without the slightest structural defect.

For Transformers who had never seen Honkai energy and knew nothing of the Herrscher of Reason, it was downright bizarre. Wheeljack and Bumblebee scratched their heads in utter disbelief.

First came the Federal capital at the North Pole, then the surrounding metropolitan clusters, spreading toward the equatorial regions, and finally extending across the entirety of Cybertron...

Constructing unfamiliar structures required a bit more time from Setsuna, which only made the visual spectacle even more overwhelming.

In just a few breaths, the desolate and war-torn Cybertron transformed into a brand-new mechanical planet...

Metallic skyscrapers pierced the sky. Factories roared to life. Across the endless cities spread a science-fiction aesthetic unique to mechanical civilization.

”Ah...”

The Transformers stared, completely dumbfounded.

Shff—

In the central districts of the cities, several massive reactors were constructed.

Dark matter reactors emitted a deep azure glow. Every Transformer could feel the immense energy contained within.

”These reactors should be more than sufficient to supply your daily operations and maintenance needs. You can compress the energy they generate into energon cubes.”

Setsuna clapped his hands.

”From now on, live well here. Autobots or Decepticons—stop fighting among yourselves.”

”!!!”

Faced with a miracle that reshaped cities in an instant, every Transformer on Cybertron stood speechless.

What was this? Magic? Something else entirely?

No one could comprehend it.

”Buddy, I already thought you were outrageous before. How come after not seeing you for a while, you learned actual magic tricks?”

Bumblebee circled Setsuna several times.

”How did you even do that?!”

”The timing was just right.”

Setsuna smiled.

If he had come earlier, he would have needed to mobilize Bulin and the Angeloids for construction. Now, with the authority of the Herrscher of Reason and the magical power provided by the Suniaster, it was much simpler.

”But I can only provide Cybertron with a framework. Its future development will still depend on you.”

”That’s more than enough. Thank you!”

Optimus Prime said sincerely.

With the complete industrial systems Setsuna had provided and advanced reactors supplying energy, steadily restoring Cybertron to its former glory would not be difficult.

Even the troublemaking and most defiant Decepticons were too stunned to speak in the face of such a miracle.

”Ahem. From now on, live properly on Cybertron. No more fighting.”

The Observer loli, seated atop her rigging, floated before Optimus Prime and Megatron.

She gestured for the two leaders to shake hands and make peace.

”Hmph—”

The two leaders were visibly awkward, glaring at each other.

”Hey, don’t be childish. I know you had grudges in the past, but the present is the present.”

Observer tilted her head.

”The Starsea Empire will continue exploring and developing this universe in the future. What kind of image is it if you keep bickering every day?”

As she spoke, she waved a tentacle.

”If anyone causes trouble again, I’ll remodel them into a bratty little girl. A mental modification, of course. We’re very good at artificial intelligence technology.”

”Optimus Prime, you wouldn’t want Megatron to turn into a bratty little girl following you around every day saying, ’Trash~ trash~, Optimus-chan is trash~, all Autobots are trash~,’ right?”

”You know I really have that ability~”

The mischievous loli pointed at Megatron.

”If you don’t believe me, ask him whether we have the ability to revive and modify Transformers.”

”Huh?!??”

The Autobots—and especially the Decepticons—stared at their leader in horror, desperate to know what had happened back then.

Optimus Prime nearly short-circuited on the spot.

”Wtf? Are you warning Megatron or threatening me?!”

—

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