"Hmm, so that's how it is."
The craft had just returned from its supersonic testing in the stratosphere. A section of its canopy had been visibly altered by the heat.
"I forgot that diamonds are vulnerable to heat."
Diamond, a crystalline form of carbon, is known to undergo chemical alteration at around 600 degrees Celsius and ignite at around 800 degrees. Jin figured the damage was caused by the high temperatures generated through the adiabatic compression of air during supersonic flight.
"I'll switch it to aluminum oxide."
Known as corundum, this mineral was the same substance that made up rubies and sapphires. While it had a Mohs hardness of 9—commonly cited as the hardest material after diamond—there were actually several artificial substances that were slightly harder.
Still, among the transparent materials Jin could currently manufacture, this was the best option for balancing hardness, heat resistance, and chemical stability. Cubic zirconia was another candidate with a Mohs hardness of 8 to 8.5, but it fell slightly short of ruby. While zirconia had higher melting and boiling points, there was a practical hurdle.
Jin could easily synthesize corundum as aluminum oxide (Al₂O₃), but cubic zirconia required adding roughly 4 to 15 percent of elements like yttrium, calcium, magnesium, or hafnium to zirconia. The synthesis was incredibly difficult, meaning he currently relied on imports from the Nord Federation.
"I'll replace the outer layer of the three-layer composite with corundum."
Jin set to work on the modification immediately. Once he finished, another point was raised.
"Father, this is not exactly a malfunction, but..."
"Did something happen?"
"Yes. Before we reached the stratosphere, I noticed clouds forming at both wingtips."
"What...?"
Jin suspected the phenomenon was trailing-edge vortices, also known as wingtip vortices—whirlpools of air created as pressure curls from the lower surface of a wing to the upper surface.
Well, the craft flies using force generators, he thought.
He had built the machine without any wind tunnel testing or formal aerodynamics, so such issues weren't unexpected. Since the craft didn't actually rely on its wings for lift, it wasn't a critical problem, but he made a mental note of it for the future.
"Understood. With that in mind, I'd like you to perform the test one more time."
"Understood."
As Jin watched the craft take off again, another thought crossed his mind.
"I should probably change the dome for No. 700672... no, for the Elder... to corundum as well."
Whether or not there was a genuine risk of fire was one thing, but now that he knew the material had poor heat resistance, his conscience wouldn't let him leave it be. So, while Reiko and Hope were occupied with their test flight, Jin enlisted the help of fifty Smiths to replace the material of the Dome.
Furthermore, just in case of a breach, he coated the interior with Ground Spider resin (GSP)—a precautionary measure even the Progenitors hadn't taken.
"You certainly are a worrywart, Jin-dono," remarked No. 700672, the Elder.
"Well, they say 'prevention is better than cure.'"
"I see. So that is your creed, Jin-dono," the Elder replied with a chuckle of understanding.
By the time they finished, Hope and Reiko had completed the second round of testing perfectly.
With the test flights concluded, it was finally time for Jin to board.
"Father, what will the name be?"
"Hmm, let's see..."
Naming was never Jin's strong suit. After agonizing over it for a while, he finally settled on one.
"Alright. Let's go with 'Sparrow'."
He chose the name simply because the craft was small. Jin engraved the word SPARROW into the craft’s dull, silver-gleaming hull.
"There. Let's go!"
Hope, Jin, and Reiko boarded the Sparrow in that order. Hope took the pilot's seat at the very front, while Jin and Reiko sat behind him. Their seats were elevated by about 30 centimeters, providing excellent visibility.
The cockpit featured transparent flooring to ensure a clear view below. Additionally, the rear blind spots were projected onto a dedicated magi-screen. While Jin was only human, Hope and Reiko possessed reaction speeds that allowed them to monitor the entire perimeter of the craft instantly.
"Taking off now," Hope declared.
The Sparrow, a specialized VTOL, floated upward with a soft grace. Under Hope's expert control, Jin's new craft began to soar freely through the skies of Hale.
"The new acceleration pressure absorption mechanism is working perfectly," Jin noted with a satisfied nod.
The system synchronized the force generator with the gravitioner to generate gravity within the craft that was equal in magnitude but opposite in direction to the force of acceleration. Thanks to this, the passengers felt absolutely nothing, even during 10G maneuvers. Combined with the constant internal gravity, it made for an incredibly comfortable ride.
Up to that point, the technology was standard. However, for this model, Jin had added a "limiter" of sorts. This specific device absorbed any acceleration pressure exceeding 0.5G (with an adjustable threshold between 0G and 1G).
This allowed the pilot and passengers to feel the G-forces during climbs, descents, turns, and rolls just enough to experience the sensation of flight without it becoming a physical burden. For comparison, a commercial airliner typically generates 0.2 to 0.3G of acceleration, while a thrill-ride roller coaster can pull between 3G and 5G.
"Oh, it really feels like I'm flying."
Jin had ridden roller coasters a few times back in modern Japan. Since those had likely hit around 3G, 0.5G was perfectly manageable. He gave Hope instructions to perform several acrobatic maneuvers, enjoying the sensation for a while.
"I suppose the maximum service speed within the atmosphere really is Mach 3..."
The wind-blocking barrier reached its limit at that speed; any faster and the resulting shockwaves would cause a disturbance to the surroundings.
"Well, considering what I'll be using it for, this is plenty. Alright, that's enough for today. Let's head back."
"...I didn't think about a hangar."
As a VTOL, it could land anywhere, but the area surrounding the House was already being meticulously landscaped as a garden. He had built the craft in the underground workshop, which was currently connected to the surface only by a ramp.
It would have been cool to launch from a cliff face like the Elder's place, Jin thought. But I suppose I'll just build a garage on the surface and launch from there.
Jin decided to stick with the "country house" aesthetic and build a garage in the yard. He opted against making it look like a secret base.
With the help of ten Smiths, the garage-style structure was finished in an hour. It featured concrete block walls, a steel shutter, and a flat concrete roof. It looked exactly like the garage Jin had envisioned.
Of course, the materials were far stronger than they appeared; everything had been reinforced with Hardening, Toughening, and Stabilize to increase durability and prevent degradation from ultraviolet rays.
"Yeah, this'll do."
The garage was wide enough to fit three cars, easily accommodating the Sparrow's five-meter wingspan. The floor inside functioned as an elevator, providing a direct link to the underground hangar and workshop.
"The Elder's home is almost finished, too. I should probably invite Marikka and Sion over."
Jin wanted to invite the dignitaries of the Northern People, given their historical ties to the planet Hale.
"And when I do, I wonder how Belialus will react..."
It was a thought that both excited and worried him slightly: how Belialus would react when he finally saw Rouge, who looked exactly like a younger version of his sister, Arshel.