Horitake's demonstration with the teacups was intuitive and clear. Even though Kagaya was not an expert in medicine or alchemy, the visual metaphor allowed him to grasp the core of the situation.
He looked at the two cups sitting before Horitake and nodded slowly.
"I see... The reason I fell into that sudden slumber yesterday was because the 'water' in my cup was replenished too quickly. My body couldn't adapt to the sudden surge, so it forced me into sleep to cope with the influx."
"Exactly, Master," Horitake confirmed.
"And as for why I feel both healthy and weak right now..."
Horitake pointed back to his teacup. "It's because the cup was just refilled to the brim. The water inside hasn't had time to settle yet; it's still turbulent. It will take a few days for the ripples to fade. Fundamentally, your body is now healthy. Your life force has been restored, and your longevity has been secured—that is the reason for the vitality and 'fullness' you feel in your blood.
"However, because your physical form hasn't fully synchronized with this new energy, your limbs feel weak, and you can't quite command your muscles yet. Just give it a few days. Let the internal storm subside, and everything will return to normal. Shinobu-san and I estimate that with your current constitution, you'll need about three to four days to fully adapt.
"After that, you will be as healthy as any normal man. You won't have to worry about the 'thirty-year-old' or 'forty-year-old' thresholds. A long, fulfilling life into your middle and senior years is waiting for you. You can grow old alongside Lady Amane. You can watch Kiriya and the others grow up. You'll be there for the birth of your grandchildren... perhaps even your great-grandchildren."
While the first half of Horitake's explanation was clinical, the latter half struck a deep emotional chord. Kagaya found himself momentarily lost in the vision of a future he had never dared to imagine.
He looked back on his life. He had been tortured by a curse that felt like a living death. Though he had always maintained a calm, serene exterior, only he knew the sheer magnitude of the agony he endured every waking moment.
For a thousand years, not a single male of the Ubuyashiki line had escaped the grasp of disease. Not one had avoided an early grave.
But that tragic cycle ended with him.
Horitake, this miraculous man, had first broken the curse, giving him hope for recovery. He had been granted the chance to outlive his ancestors, to be a husband and a father for a little while longer.
And now, Horitake and Shinobu had gone even further. They had developed a potion that replenished his very essence!
What did this mean?
It meant longevity. It meant he was no longer a man on borrowed time. He could finally grow old with his wife. He could have a happy, quiet retirement. These were things he hadn't even dared to hope for, let alone pray for.
And now, they were his reality.
The physical weakness in his limbs was a small price to pay for the absolute certainty of health that resonated in his chest. It wasn't a dream. He truly would live.
The weight of the moment overwhelmed him. His voice trembled, thick with emotion. "Horitake... I am far happier, and far luckier, than any who came before me."
"Master, you give me too much credit..."
Faced with such raw emotion, Horitake didn't quite know how to comfort him. He could only repeat humble platitudes.
Fortunately, Kagaya was a man of extraordinary mental fortitude. The intense wave of emotion passed as quickly as it had arrived. He steadied himself and looked at Horitake and Shinobu, turning the conversation back to the task at hand.
"In truth, this miraculous potion was not primarily intended for me. It was created for the Pillars—for the swordsmen who awaken the Demon Slayer Mark. Horitake, Shinobu... how difficult is it to produce more of this?"
Since Shinobu had handled the bulk of the lab work, she took the lead on the answer. She thought for a moment before speaking.
"Master, I will be honest: the difficulty of producing this potion is significant."
"What are the specific hurdles?" Kagaya asked.
"There are two main difficulties. The first is the raw materials. The formula is incredibly complex and requires several rare and precious medicinal herbs that are worth their weight in gold. Some of these can no longer be found within Japan and must be imported from China. When you factor in the procurement and processing costs, the price of a single dose is astronomical."
Money, however, was of little concern to Kagaya. He waved his hand dismissively.
"That is no issue. Anything that can be solved with money is not a problem. No matter how rare the herbs or how difficult the import process, the Demon Slayer Corps will secure them. Price is irrelevant."
Horitake couldn't help but look at Kagaya with a bit of envy. He wondered if he would ever reach a point in his life where he could casually wave away a fortune with a single sentence.
Shinobu continued, "The second hurdle is the manufacturing process. Synthesizing the Life Supplement Potion is an arduous, delicate, and multi-staged operation. It isn't something that can be taught to an average apothecary. Even with Horitake and me working together and having researched it for so long, we only just managed to produce this one bottle. Of course, now that we have a successful blueprint, subsequent batches will be slightly easier, but they will still require a vast amount of time and focus."
This was a problem money couldn't solve. Kagaya fell into a thoughtful silence.
Horitake chimed in from the side. "Because of how vital this potion is to our strategy, we have to keep it strictly confidential. We can't let word of its existence get out. This means the production team is limited to just Shinobu-san and myself. We can't set up an assembly line or delegate it to the Kakushi. Our efficiency is naturally capped. We ran the numbers yesterday; if the two of us dedicate ourselves entirely to production, it will take about half a year to create enough for the Pillars."
Kagaya's eyes widened slightly. "It requires that much time?"
"Yes, Master. Currently, the Corps has ten Pillars—myself and nine others. If I'm not mistaken, by the time the final battle arrives, all ten of us will likely have awakened the Mark. My specific Mark does not drain my lifespan, so I don't need the potion. But the other nine do. At a bare minimum, that's nine bottles. Shinobu-san and I can produce roughly one bottle per month if we work at full capacity. That means nine months of continuous labor."
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