Kai’s skeleton was composed of an alloy of aluminum, copper, and magnesium.
In common terms, it was an aluminum alloy known as "Super Duralumin."
"Uni is rich in aluminum, isn't it?" Jin asked.
『Yes, My Lord. That appears to be the case,』 Laojun replied.
That explained the choice of material.
"Hmm, I haven't developed any aluminum-based magi-alloys yet..."
Jin decided to take a brief detour into researching aluminum alloys.
"First, the standard addition of mithril."
He began by replacing half of the copper content with mithril.
"I see. It really does get reinforced."
The degree of magical reinforcement clearly increased.
"Well, I don't have much time, so I'll stop once I've determined the optimal amount of mithril to add."
Since modifying Kai was his primary objective, Jin didn't want to squander too much time. He performed a series of rapid experiments.
"Hmm, so the original ratio was actually the best."
Super Duralumin is typically composed of 94 percent aluminum, 4.5 percent copper, and 1.5 percent magnesium.
He discovered that by replacing half of that copper—2.25 percent—with mithril, magical reinforcement was achieved most efficiently. It resulted in roughly two and a half times the original strength.
"I’ll call it magi-duralumin."
Since there was almost no change in volume, he proceeded directly with the spells Add and Alloying.
"No matter how many times I see it, Jin-nii's work is incredible," Elsa whispered in admiration.
To her, Jin seemed almost god-like when he handled metals. The primary factor behind this was likely a combination of the metallurgical knowledge he had acquired in modern Japan and the fact that he naturally excelled at—and truly loved—metalworking.
Returning to the task at hand.
Having finished the development of the magi-duralumin for Kai, Jin turned his attention to the muscle tissue.
"Given the strength of the skeleton, standard components should be sufficient."
"Mm, I agree."
The standard components were made from ground spider silk bundled using a special twisting method. Even these could produce two to five times the output of a general-purpose golem—and depending on how they were utilized, nearly ten times.
"Next is the control core upgrade."
He decided to replace the old core with an all-attribute magi-crystal of Hourai Island’s standard grade, which would be considered an advanced-level item by the rest of the world.
"I should replace the magi-nerves as well."
Jin systematically upgraded various key points and implemented countermeasures against Master-Slave Magic before reassembling the unit. The work was completed in approximately two and a half hours.
"Looking at it now, it seems this Kai was manufactured on Uni using the technology of the Former Leonard Kingdom."
"Jin-nii, how can you tell?"
"Well, the password was just 'Leonard' spelled backward. That made me suspect the creator was someone affiliated with the old kingdom."
"Oh."
"Well, it's just a guess. I might be wrong."
As he spoke, Jin prepared to restart Kai.
"That should do it. Wake up."
"Yes, Master," Kai replied, sitting up. His movements were far smoother than they had been before the modification.
"How are you feeling? Any issues?"
Kai performed a self-diagnostic before answering.
"Everything is excellent. Thank you very much."
"Good. Please continue to look after Lady Milowina."
"Yes, I understand."
Thus, Milowina’s personal golem was granted superior performance and returned to her service.
"Now then, one more thing."
"Jin-nii, there's more?" Elsa checked the clock and frowned slightly.
"It’s okay. This will be quick. I want to make a Fellowship Bracelet for Lady Milowina."
"Oh, I see. That makes sense."
Since it was a task he had performed many times, he finished it in short order. He chose a design featuring gold stripes over a silver base.
"Alright, finished."
Having finally completed everything he set out to do, Jin went to bed with a profound sense of satisfaction.
The next day, July 2nd.
After breakfast, Jin presented the Fellowship Bracelet to Milowina.
"My goodness, Jin-kun, what is this?"
"It’s called a Fellowship Bracelet. It can generate a barrier, and it also functions as a personal ID and a communication device. Oh, and it can serve as a light, too."
"My, how wonderful. Thank you, Jin-kun."
"The most important feature is that Laojun can remotely deploy the barrier for you. It provides peace of mind even if we happen to overlook something on our end."
As Jin explained the functions, Milowina memorized them instantly.
"Also, I've made some improvements to Kai, so he should be even more effective as a guard."
"...Jin-nii," Elsa murmured.
She thought he didn't have to put it so casually, as if he had merely polished the golem a little.
Is he doing that so Lady Milowina doesn't feel too indebted? she wondered.
Realizing this might be the case, Elsa kept her thoughts to herself. Whether her guess was correct or not, she couldn't say for certain. However, Milowina was genuinely delighted by the news, so it was hardly an issue.
"Thank you for everything, Jin-kun. Kai, I'll be counting on you even more from now on."
"Yes, Lady Milowina."
At noon that same day, a report reached Jin.
『My Lord, Land 51 reports that they have discovered ruins in the middle reaches of the Neto River.』
"Oh, they found them!"
Having just finished lunch, Jin hurriedly gulped down his tea, left the cleanup to Soleil, and headed for the command room with Reiko. He cast Cure on his slightly scalded tongue as he went.
Elsa and Milowina decided to finish their tea at a more leisurely pace before following him.
"...I see. If that's the case, then the outlook is a bit grim."
When Elsa and Milowina arrived at the command room, they found Jin looking disappointed. Elsa spoke up, concerned.
"Jin-nii, what happened?"
Jin turned to face them.
"...It seems there's little hope for the first ruins."
Elsa peered at the monitor, and once she saw the footage being displayed, she understood his reaction.
"...This is terrible."
"Isn't it?"
The site where the ruins were believed to be was riddled with holes. It looked as if a massive excavation had taken place decades—perhaps even a century—ago. Whether it had been the work of treasure hunters seeking ancient relics or a mining operation targeting underground resources was no longer clear.
"The passage of time is a frightening thing," Milowina remarked as she looked over their shoulders. It was clearly painful for her to see her homeland ravaged in such a way.
The holes were a mix of vertical shafts and diagonal tunnels, making the site look somewhat like a massive ant-hill.
"The Former Leonard Kingdom was rich in minerals, so this might have been a mine," Jin muttered.
"Jin-nii, how could you tell this was a ruin if it's been destroyed this much?" Elsa asked.
"Oh, that's because..."
Jin gave a signal, and the screen changed.
"Ah..."
The monitor now showed the Land squad. They were holding something in their hands.
"Are those... fragments of the ruins?"
The pieces varied in size, but they were all made of a dense, whitish stone with characters engraved on the surface. Since the fragments were scattered, it was impossible to read the full text, but words like 'Record,' 'Leonard Kingdom,' and 'Preserve' were visible here and there. It was likely that they had once been part of a mural.
Other Land units were holding components from a decayed Magi Machine. Judging by the barely legible magi-formula, it had likely been a magi-brain originally.
"It’s hard to conclude anything else, isn't it? It's a real shame."
The Land units had searched the surrounding area and the underground, eventually discovering these items in a large subterranean hall and a hidden room located further back.
"Jin-kun, these things happen," Milowina said, surprisingly unfazed. "Perhaps it's because I've already seen the ruins in Diaa and Karnag."
She seemed to have accepted the impermanence of all things.
"And it's also thanks to seeing the people of Kaina Village."
Milowina explained that the continuation of human life was the true evidence of her own legacy.
"Being able to entrust what you have built to someone else is a form of happiness," she said.
More so than leaving behind records, and more so than building monuments.
As if offering him a final piece of wisdom, Milowina smiled and told Jin that leaving behind a successor might be the true raison d'être of a human being.