Early the next morning, Jin finished his meal and immediately set to work on crafting the proliferation-model automobile.
The most critical area requiring modification was the reduction gear.
Modern Earth vehicles required complex transmissions, but Jin didn't know their exact internal structures. Consequently, his reduction gear consisted of only a single stage. His plan was to take the output of a smaller, lower-output Golem Engine and use gears to reduce the speed while simultaneously increasing the torque.
He set the reduction ratio to 1:5.
This allowed the engine's torque to be reduced to one-fifth, which in turn meant the physical size of the engine could be scaled down significantly. While calculating the exact dimensions to maintain specific horsepower was a complex task Jin wasn't entirely confident in, he initially considered making the engine one-fifth the original size. However, he quickly reconsidered, realizing ten centimeters was far too small.
"Let’s go with twenty centimeters."
If he based the calculations solely on the strength of the magical muscles, this was almost the perfect size, as muscular force is proportional to cross-sectional area.
With Elsa and Reiko’s assistance, he completed a twenty-centimeter-class Dual Golem Engine. He intended to mount this in the automobile and configure it to be slowed by the reduction gears.
"Modifying the existing one would be a hassle, so let’s just build a new one from scratch," Jin said, his nature as a creator on full display. He figured the vehicle he had finished the day before could be reserved for use on Hourai Island or Kunlun Island, so the effort wouldn't be wasted.
Since he had already built one prototype, the proliferation-model test car was finished in a remarkably short time.
"Now then, let's see how the power holds up."
When he took it for a test drive in the plaza in front of the laboratory, he felt a distinct lack of power during initial acceleration.
"Maybe 1:5 isn't the right gear ratio..."
Thinking 1:10 might be overkill, he adjusted it to 1:7. Specifically, he reduced the number of teeth on the pinion gear—the gear attached directly to the Golem Engine.
During this process, he ensured that the number of teeth on the meshing gears were coprime, meaning their greatest common divisor was one. When gears are coprime, the teeth mesh evenly over time and wear down at a uniform rate, which helps maintain the vehicle's long-term performance. Jin settled on 13 teeth for the Golem Engine side and 90 for the axle side.
"Oh, this works well."
The change effectively resolved the lack of power during acceleration.
"As for the top speed... well, I suppose this is sufficient."
Even with the accelerator floored, the car only reached about twenty kilometers per hour—roughly the speed of a human running.
"There's no danger at this speed, and people can just view it as a novel toy."
It was a perfectly adequate speed for moving around a city. Using this configuration as his base, Jin decided to move forward with the automobile he would offer to the Empress.
The power system and suspension would be identical to the second prototype. The seats were upholstered in magical beast leather, stuffed with Gula Schwamm to maximize comfort. The main challenge was the body design. He intended to make it look like a proper Horseless Carriage.
Elsa assisted with the design. They constructed the body primarily from bronze and wood, applying gold plating to key areas to give it a sense of imperial luxury. After all, this car was destined for the Empress herself. Since it was intended for her exclusive use, he placed the Imperial family crest, the Drei Schwerter, on the sides.
"Yes, this turned out beautifully."
A literal "Horseless Carriage" was complete.
"Next is the driver golem."
He used bronze for this as well, crafting the unit in the form of a young man. He incorporated various servant-like functions, such as opening doors for passengers. He decided to call this type of golem a "Fahrer," following the Shouro Empire's term for a coachman. Since this was the first unit of its kind, it was designated Fahrer 1.
He then installed various equipment to finalize the build. To ensure he hadn't missed anything, Jin compared it to his memories of cars from modern Japan. Although Jin didn't have a driver's license and wasn't exactly an enthusiast, he had frequently ridden in taxis for work and in cars driven by colleagues, so he knew the essentials.
"Ah, it might be good to include wipers."
This comparison proved quite effective, helping him recall features he had originally overlooked. After spending the entire morning on refinements, a one-of-a-kind luxury automobile was finished.
"...With this, mass proliferation is going to be impossible."
"...Yeah."
Elsa, who had been assisting him, agreed completely. By fussing over every detail for the Empress’s personal vehicle, they had created something far beyond the reach of commoners—and even most nobles.
For instance, the headlights were not simple lantern-style magi-lamps; instead, he had used "Light" magic and modified it to have directional focus. Then there were the windows. Every large pane was made of high-transparency quartz glass. For safety, they were reinforced with Toughening to create "toughened glass" that wouldn't shatter even if struck by a stone.
He also lowered the driver's seat slightly, positioning it so it wouldn't obstruct the passengers' view, drawing inspiration from modern tour buses. The horn was not a harsh, piercing noise, but a pleasant tone like a loud bicycle bell, achieved using a recording and playback magic tool developed by Elsa.
He even built in a miniature refrigerator, allowing for cold drinks in the summer, which could be switched to a warming box in the winter. Four spare tires were stored beneath the floor.
As for performance, the top speed remained at twenty kilometers per hour, intended strictly for use within city limits or the immediate outskirts. Excluding the driver golem, the car could seat six people in a three-plus-three configuration. The seats could rotate and recline, allowing passengers to sit face-to-face, face forward, or even lie flat for a nap.
Regarding the mana supply—the vehicle's fuel—the installation of a large mana tank ensured it could operate for two consecutive days.
"Shall we make an improved mana supply machine as well? A 'mana server'?"
Jin figured such a device would be necessary if they intended to introduce more lifestyle-improving magic tools in the future. Hearing this, Elsa asked if she could try making it.
"Jin-nii, let me handle that."
Since it wasn't a particularly complex project, Jin nodded.
"Alright, give it a try. Just don't make it too compact; it's better if it has some size to it."
The mana supply machines currently in use were roughly the size of an office desk. Jin advised her to keep it only about two sizes smaller than that.
"Understood."
Jin watched Elsa work, idly reflecting on human psychology—how if something is made too small, people often lose their sense of appreciation for it and handle it carelessly.
"You've really improved, Elsa."
The praise slipped out naturally.
"Th-thank you."
Elsa was visibly flustered by the sudden compliment, and a magi-crystal slipped from her hand.
"Oops."
"That was close."
Reiko caught the crystal before it hit the floor. Jin awkwardly pulled back the hand he had reached out.
"Thank you, Reiko-chan."
"You are welcome."
Elsa returned to her task, and in about thirty minutes, the mana server was complete.
"It’s a job well done. Good work, Elsa."
"Mm, thank you."
"...Wait. Hold on..."
As he stared at the finished mana server, Jin was suddenly struck by an idea.
"Jin-nii, what's wrong? Was something... wrong with it?"
Elsa's voice sounded anxious, but Jin simply patted her on the shoulder and smiled.
"We should just install this on the car!"
"What?"
"If we do that, it can keep running forever without ever needing to be refilled!"
In essence, the mana server was a giant ether converter.
"Ah, I see!"
Elsa understood immediately and broke into a wide smile. They installed the mana server into the vehicle, granting it semi-perpetual operation.
Just then, Loll arrived to inform them that lunch was ready.
"Master, the midday meal is prepared."
"Oh, is it that time already?"
The timing was perfect. Jin and Elsa washed their hands and headed to the dining room. Reiko followed them—or rather, followed Jin—while Edgar tidied up the workshop before joining them a moment later.
"Oh, it's udon today?"
Today's lunch was tempura udon.
"Yes. I prepared it myself after learning the techniques from Perido and the others," Loll explained.
"Hoh."
The shrimp and vegetable (a pumpkin substitute) tempura was fried to a crisp, and the flavor of the broth was perfectly balanced. The udon was slightly soft, though Jin couldn't tell if that was due to the flour blend or the kneading technique. While Jin usually preferred firm, chewy udon, Elsa seemed to love the texture of this batch, even going back for seconds.
"Now then, shall we make an automobile for ourselves as well?"
"Mm."
After lunch, Jin and Elsa set to work on a high-performance version of the automobile. While the appearance of the engine and suspension would be identical to the public version, the materials would make it far more powerful. By using orichalcum instead of bronze for the Golem Engine and Hourai Island's standard-grade magical muscles, they could expect roughly five times the power.
By omitting the ornate decorations, the car would also be slightly lighter. However, Jin made sure to paint his crest—the "Maru ni Futatsu-biki"—prominently on both sides and the roof. He decided to train Edgar to be the driver.
"The problem is how to transport these to Loizart."
Each vehicle weighed approximately five hundred kilograms, making them a bit too heavy to load onto Konron 2. Laojun then offered a suggestion.
"My Lord, we should simply act as though we built them at the mansion in Loizart."
"Ah, you're right. It'll be much easier to transport them to the Imperial Palace from there anyway."
Jin readily adopted the plan.