"Hey, Laojun, it's an established fact that Onii-chan went four hundred years into the future once, right?"
One day on Hourai Island, Hanna was posing a question to Laojun.
『That is correct. After all, My Lord himself—who returned from four hundred years in the future—said so.』
"I thought so..."
Hanna was lost in thought.
It was now the year 3467, and Hanna was nineteen years old. She had blossomed from a beautiful girl into a stunning young woman.
Looking at her, Reiko had remarked that she was a perfect lookalike of the Predecessor Magi Craft Meister, Adriana Barbora Tsetse.
"It's possible to send objects into the future, isn't it?"
『It is. What My Lord calls a "time capsule" is a prime example.』
If a container like a mana tank, which prevents its contents from deteriorating, were preserved for a long duration, it could be considered a gift to the future.
However, Hanna was envisioning a transfer across time itself.
Hanna had always enjoyed pondering such theories, regardless of whether they could actually be realized. Perhaps because she was surrounded by men of action—or rather, because everyone else was almost exclusively focused on the practical—she was growing into a scholar who preferred theoretical development.
"Hmm, that's a bit different from what I mean..."
Transferring things to the future in the manner of a time capsule was far from what Hanna was looking for.
"Reversibility... I want to find a method with that possibility. I want to develop it."
『Reversibility, you say...』
Laojun interpreted "reversibility" in this context to mean "receiving" in response to "sending." In other words, Hanna was attempting to transcend time.
"...Is it impossible?"
『No, Hanna-chan. The fact that My Lord returned from the future means that a way must exist.』
In short, there had to be a method. Since Jin had returned to his original time, it likely meant that a future Laojun had taken some form of action.
Laojun firmly believed that the research Hanna was currently pursuing would eventually lead to the very means of sending Jin back to his original time from four hundred years in the future.
The goal was to somehow manage sub-ether... to handle it freely, or at least to a certain degree.
"Hmm, I can handle sub-ether just a little bit, but it's still not enough."
Hanna tilted her head cutely.
"The hardest part is the destination. It's like trying to hit a tiny little island in the middle of an infinitely vast sea called the 'future' with an arrow... maybe even harder than that."
Laojun was the one to offer advice.
『Hanna-chan, there is one possibility.』
"Eh? Laojun, what is it?"
Knowing it was Laojun speaking, Hanna knew it wouldn't be a frivolous idea. She abandoned her musings and listened intently.
『The "stones" that My Lord brought back from that other world.』
"Ah..."
Thinking they would serve as a memento, Jin had brought back walnut-sized white, blue, and red stones from the other world.
Laojun explained that those stones emitted ether waves, and with the proper means, they could serve as markers.
『However, it might not be of much help.』
"No, that's not true at all!"
Hanna insisted that being able to identify the "world" alone was a major step forward.
"Now it's just a matter of identifying the timeline..."
『That would be the case. Regarding this, when My Lord went four hundred years into the future and returned here, he brought those stones back with him.』
At that point, the ether waves in the future should have vanished. In other words, it wasn't an infinitely long "straight line"; the other end of the signal had been cut off.
That point of disconnection was precisely the moment Jin had departed from four hundred years in the future.
"Wait? But if that's the case, those stones exist 'now,' don't they?"
『Yes.』
"Then, for a certain period in the future, did those stones overlap?"
『There is no way to confirm, but it is a possibility. Another possibility is that they decayed and vanished during those four hundred years, so they did not overlap when My Lord appeared there.』
"Hmm..."
In any case, Hanna concluded for the time being that there would be a discontinuity.
"Well, even so, it's become much easier to aim now."
Hanna let out a small sigh of relief.
Laojun also rejoiced that Hanna's research had gained momentum. After all, in four hundred years, it would be Laojun's responsibility to send Jin back to the past. The knowledge required for that task was still far from sufficient.
Laojun had already received a transfer of the knowledge Jin had gained in the other world, but it was so far removed from the laws of this world that it was difficult to find any common ground.
(『As expected, it will be difficult without Hanna-chan's cooperation...』)
To solve this within the limited timeframe of four hundred years, Laojun judged that the cooperation of Hanna, who possessed a rare brilliance, was indispensable. This had also been corroborated by the returned Jin, who noted that Hanna's intellect had been essential for research into ether waves.
＊ ＊ ＊
Hanna continued her experiments throughout the day.
Since Jin was away in Loizart, she had enlisted the help of Laozi and the Smiths to construct a sub-ether wave generator.
She had made something similar a short while ago, but this one was more compact and designed to operate with greater precision—or so she hoped.
Regardless, nothing could begin if they couldn't freely generate and receive ether waves. The research of Hanna and Laojun had only just begun.
"Hmm, if I can't control and receive this exactly how I want, things like 'Full Dive' will remain a pipe dream..."
The "Full Dive" Hanna spoke of was a method for controlling automata that she had been researching recently—specifically for the new model Doppels.
She envisioned an automata that one could synchronize with even more deeply than current Doppels, or perhaps a "vessel" into which one's very "will" could be transferred.
This was another technology Hanna was exploring alongside time travel. Unlike No. 600012, who had once opposed Jin, Hanna wasn't aiming to transfer knowledge to an automata to prolong her life. Instead, she sought a form of "piloting" where she could return of her own accord.
"Ah, there are so many things I want to do, and time is so finite..." Hanna lamented.
Just then, Jin returned from Loizart.
"What is it, Hanna? Something troubling you?"
"Ah, Onii-chan!"
Even at nineteen, Hanna still called Jin "Onii-chan."
"You see, I was just worrying about how I have so many things I want to accomplish but so little time."
Hanna was always honest with Jin.
"Lately, I've been thinking how nice it would be if there were several of me."
At her words, Jin offered a smile.
"Hahaha, that's so like you, Hanna. But if you were split into several people and each one went off to accumulate different experiences, wouldn't they eventually stop being 'you'?"
"Eh?"
Hanna didn't understand what Jin meant for a moment, but she eventually grasped his point.
"Hmm, I wonder? But that's a philosophical question about what constitutes the self and the ego, isn't it?"
"I suppose so."
"I think of it like this... If a person possesses the elements that make others recognize them as that person, then they are that person."
"Eh?"
This time, it was Jin's turn to take a moment to process.
"Hmm... I see. That's an interesting perspective."
As Jin expressed his admiration, Hanna added another thought.
"Onii-chan, you sometimes overhaul the things you've made, right? So I think you'd understand."
"...Ah."
Spurred by Hanna's words, Jin realized it too.
Take Reiko, for example. He had completely renewed everything from her skeleton to her muscles and skin, yet Reiko was still Reiko. What, then, was the defining factor that made him recognize her as Reiko?
If he were to create an identical automata, including a perfect copy of the control core, would that also be Reiko?
"...I feel like this is definitely going to turn into a philosophical debate."
Jin gave a wry smile as he recalled past events.
"...Come to think of it, both the old and new No. 600012 recognized each other as 'No. 600012'."
Ultimately, Jin reached the tentative conclusion that it probably came down to how a third party perceived the individual.