If an object's parts are replaced, is it still the same object?
In Reisen Riou's previous world, around the 1st century AD, Plutarch posed a question: if Theseus's ship had every plank replaced, would it still be Theseus's ship?
This became known as the "Ship of Theseus" paradox in Reisen's old world—one of the oldest thought experiments, a riddle of identity.
It was so famous that many philosophers weighed in, and Reisen had a deep grasp of it.
Not that he knew the answer. Some questions, especially philosophical ones, never have one.
"These philosophy problems are the worst," Dottore grumbled, stuck in a mental loop before snapping out. "They're for the sharpest minds. We're just scholars with some talent."
"Your theory's a bit extreme," Reisen chuckled. "Not denying it, mind you. If you tested it on death row inmates, I'd have no issue."
"But our test subjects are, to some extent, our own people."
"We can't go full brute-force."
"Fact is, some civil official families have been backing Smart Drug research."
"Their labs are under your Human Research Institute," Reisen said slyly. "You might not believe it, but they're outpacing Sumeru's progress."
These families were ruthless. Over four generations, they'd refined Smart Drugs to enhance brainpower.
They also used drugs and secret elixirs to tweak their bodies, boosting Smart Drug absorption and brain development.
These families had little standalone clout but held many high-ranking scribe roles in the Three Commissions and Shogunate.
Some even became Inazuma's renowned scholars.
"Here's their Smart Drug data. Make it more universal, and plenty of dimwits will thank you in the future," Reisen said.
Dottore ignored him, diving into work.
…
Reisen didn't tell Dottore his theory was both right and wrong.
Sensing laws did rely on the sixth sense, but in Teyvat, it had another name: Soul Perception.
Enhance the soul, and you boost Soul Perception.
But souls were the toughest human attribute to improve in Teyvat.
Reisen was a pro at fixing soul damage but a novice at enhancing souls.
Notably, the best soul enhancement methods were study and meditation, tied to Teyvat's two main cultivation paths: magic and martial arts.
Drugs could strengthen souls by stimulating a brain region, tightening the body-soul link, then reinforcing the soul via the body.
This often depleted the body—a dead end for most.
Exceptions existed, like the Smart Drug families. Through crude research, they'd learned to toggle the body-soul connection with drugs and rituals.
This let them safely boost brain and soul. Body energy? They were weaker there.
They'd need a few more generations to perfect it.
For now, their Smart Drugs, paired with Reisen's alchemy, sufficed for perception enhancement.
Reisen's alchemy was a Raiden Makoto-approved version, stripped of most ley line and Abyss knowledge but still potent, supplemented by his own expertise.
Rumor had it the original came from Khaenri'ah's Royal Knights. Reisen wasn't sure, but the seller claimed so, and the tech was impressive.
Khaenri'ah's fall was Reisen's gain.
This alchemy added nodes in the body to convert physical and soul energy, mainly in nerve-rich areas.
Since samurai had robust physical energy and recovery, Reisen used small, frequent doses of physical energy to feed soul energy.
This gently boosted the soul, and with Smart Drugs, unified the body's alchemical nodes.
The result: enhanced Soul Perception.
The procedure cost about 100,000 Mora, solving two issues: laying the groundwork for Longevity Surgery and opening life limits for breakthroughs while boosting perception.
Best part? It minimally altered the body, preserving fertility.
Breaking life limits didn't help LV70+ powerhouses much—it was a side perk, mainly for weaker fighters.
Unlike Longevity Surgery, this procedure wasn't top-secret. Reisen gathered shrine maidens for live training.
His teaching outshone the One System, Ten Thousand Minds Machine. Version 10.4's data transfer was a third of his original capacity.
After multiple life transformations, his transfer ability was over 300 times stronger than version 10.4 and 100 times better than the machine's initial version.
Reisen trained most maidens in three surgeries, then bolted. The rest was their job.
Dottore bailed too, finishing a surgery and following Reisen, claiming to "keep pace with the boss," though he often cursed Reisen's lax time sense in private.