"...Jin-nii, this is amazing. Thank you."
Having successfully absorbed Jin's knowledge—even if it was only the beginner-level material—Elsa was uncharacteristically giddy.
"...The structure of matter, why things fall, why airplanes fly... I finally understand."
Elsa had gained scientific knowledge roughly equivalent to a middle school level. She was flushed with excitement, the joy of finally understanding things that had long been mysteries to her making her pulse race.
"Now you're officially my disciple, Elsa. But let me warn you, don't go around boasting about it, okay? Exercise some self-restraint."
"Self-restraint... Jin-nii, are you really the one to say that?"
Jin found himself unexpectedly teased by his pupil.
With a wry smile, Jin scratched his head and returned to their original purpose.
"Well then, the bed and futons are finished, but we can't exactly carry them out of here..."
They were far too large to fit through the carriage's Warp Gate.
"Father, I believe we have no choice but to pack them properly and transport them in secret," Reiko, who had been silent until then, suggested.
"Yeah, I guess so. That's the only way..."
Consequently, they decided to transport the gifts in the middle of the night using an aircraft enchanted with Invisible.
"Maybe I should build a submersible base around Lake Tosmo as well..."
Upon hearing Jin's mutterings, Laojun would actually end up constructing one later, but that is a story for a bit further in the future.
"Now then, I suppose this will do?" Jin murmured as he looked over the bed and futons intended as a gift for Reinhard.
At that, Elsa made a request of him.
"...Jin-nii, I want to give Rai-nii and his bride a gift too."
"Ah, that's right. You want to offer your own congratulations, Elsa. So, what did you have in mind?"
Elsa answered the question immediately.
"A mascot."
"A mascot?"
Elsa explained to the questioning Jin. In her culture, there was a custom of gifting dolls to protect a new household. When her eldest brother, Moritz Randol von Amber, got married, Reinhard’s mother had gifted him one.
"I want to make a doll like Non and give it to them."
Non was the Ichimatsu-style Japanese doll Jin had given Elsa for her birthday. Elsa cherished it and still kept it on display in her room back in Kaina Village.
"I see. Give it a try. You can use any materials you like."
That said, a small doll wouldn't require a vast amount of resources.
"If there's anything you don't understand, I'll teach you."
"Yeah. I'll try."
So, leaving things to Elsa's initiative for the moment, Jin decided to finally set about his other objective: upgrading Reiko.
"Reiko, you saw Ar earlier, right? I want to add that same sense of touch to you. What do you think?"
Reiko nodded.
"Yes. I have no objections to anything Father deems for my benefit."
"Good."
Jin called out to Elsa, who was working hard on her own project, and then headed to the second-floor laboratory with Reiko.
The material for the tactile sensors was the wing membrane of a Sea Dragon.
The wing membranes of dragon species are moved not by muscles, but by magic. In other words, they can be controlled freely through mana. When spread out, the membrane is stronger than steel despite being only about a millimeter thick. Conversely, when folded, it is soft enough to offer no resistance.
By utilizing this characteristic, Reiko could make her skin harder than steel or more supple than a baby's skin depending on the situation. Furthermore, it was known that magic was generated when the membrane was stretched, contracted, or bent. This applied to all magical beasts and monsters with wing or feather membranes, not just true dragons.
However, the materials available during the Predecessor's era were inferior to the feather membranes of a Sham Dragon or the wing membranes of a Sea Dragon, and the magic generated was weak. Even the Predecessor had not thought it could be put to practical use.
But Jin believed the skin itself could serve as a tactile sensor.
"Hmm, so that means I need to distinguish between the magic generated when the skin deforms and the magic Reiko herself emits."
After thinking for a while, Jin realized that the patterns of Reiko's own magic and the magic generated by the skin would likely be distinct.
"Alright, Reiko, sit over there for a moment... Let's see, try clenching and opening your hands."
"Yes, Father."
Jin used Trace and Inspection simultaneously to follow the flow of magic.
"I see..."
Jin captured the extremely minute flow of magic emitted by Reiko's skin and began his analysis. He repeated the process for fifteen minutes.
"Alright, I've got it."
Through this investigation, he discovered that the difference appeared not as a flow, but as a difference in potential. The greater the deformation, the higher the mana potential. By reading this mana potential, the amount of deformation could be determined, which meant the force applied to that specific area could be calculated.
Jin imagined a thermographic image. Those showed high and low-temperature areas color-coded; this would show high and low mana potential.
"In that case, I'll need a magi-device that can read that distribution..."
Until now, it had been enough to simply read the physical deformation of the body. That could be done by reversing the flow of a Forming spell, but a device that read the distribution of mana potential was a world first.
It was a first for Jin as well—a device that would bring a revolution to automata. He carefully thought through the magi-sequence and began combining the magi-formulas.
"The basics are Trace and Inspection. I'll apply those, take the data in, then perform weighting and position back-calculation..."
Muttering to himself, Jin slowly but surely completed the new magi-device. It was a piece of equipment consisting of complex magi-formulas comparable in density to a control core.
"...It's finished."
Exhausted, Jin murmured as he leaned back into his chair.
"Father, thank you for your hard work. Um... it is already night. I believe it would be best to stop for today."
Surprised by Reiko's words, Jin looked out the window. It was pitch black.
"It is past seven o'clock."
Thanks to the Ether Lights that automatically lit up when it got dark, he hadn't noticed the passage of time at all.
"I see. Well then, let me install this in you before we finish."
"Yes, I understand."
The integration into Reiko was finished in about a minute.
"It's not linked to your movements yet, so it shouldn't be difficult to move. For now, just focus on data collection."
"Understood."
Reiko nodded obediently. Jin finally took proper note of the hour.
"Ah, that's right, what about Elsa!?"
He hurried downstairs, where he found Elsa also completely absorbed, continuing to work on the prototype of her mascot.
"Hey, Elsa."
When Jin called out, Elsa stopped her hands and looked up as if coming back to her senses.
"Ah, Jin-nii."
"I just realized it myself, but it's already seven o'clock. Let's call it a day and have dinner."
"Yeah... I'm hungry."
Blushing slightly, Elsa stood up, brushing the dust from her hands and clothes.
"...I think I understand a little of how you and Rai-nii feel now."
Elsa spoke softly, her face turning even redder.
"Haha, well, I'm glad to hear that... though I'm not sure if that's a good thing."
She was referring to how Jin and Reinhard would sometimes neglect their meals to focus on crafting. Until just recently, Elsa had been the one rebuking them for it.
Jin and Elsa returned to Kaina Village via the Warp Gate. The time difference between Kaina Village and Hourai Island was about two hours; in the village, it was just about time for dinner.
"Welcome back, Jin-sama. Welcome back, Elsa. Dinner is just ready."
Mine came out to greet them.
"...Ah, I see. So this is the time difference."
Elsa, with her new scientific foundation, was able to grasp the concept immediately. Jin looked forward to seeing how she would use that knowledge in the future.
"Honi-hyan, welcome back."
Hanna also greeted him with a smile.
Even if it was in a slightly different form than his friendship with Reinhard, he had his family here. The thought warmed Jin's heart.