The next morning.
I followed the guidance of Shutara Senjumaru to her workshop.
"Welcome to my sanctuary. To my workshop."
"Hoh..."
The interior was surprisingly spacious.
Inside, the parts of dolls were laid out in rows. Within the unfinished automatons, tiny gears clicked and ground against each other as they rotated in sync.
This was the Sengoku period, a time before Western influence should have taken root, yet such technological prowess was on display.
It felt as though I was looking at something out of a steampunk fantasy.
While I was slowly taking in the sights of the workshop, Shutara Senjumaru brought forth two particular dolls.
"These are the fruits of my labor: Demon Slayer Edge, Type 0 and Type 1."
Two wooden dolls. Both were dressed in the Demon Slayer Corps uniform, each clutching a Nichirin Blade.
"Type 0 mimics a swordsman of the 'Flame' school, while Type 1 is capable of replicating the movements of a slayer who utilizes Flame Breathing."
Oh!
"Do these truly move?"
"Indeed. Type 0 can perform fifteen distinct movements, and Type 1 can execute thirty-one."
They're moving robots! And bipedal ones at that!
Shutara Senjumaru carried the two dolls outside.
"Well, if they were to activate inside the workshop, they might very well shatter all the delicate components housed within."
She then picked up an object with her prosthetic hand and moved behind the dolls.
"To awaken these puppets, a key is required."
She pulled down the collars of the dolls' uniforms. Beneath the fabric, a single hole was visible in the center of the doll's back.
Wait, that key... I've seen that shape somewhere. It looks like the kind of wind-up key you'd see stuck in the back of a Nutcracker. Surely not...
She inserted the key into the hole.
*Click! Click!*
She turned it several times, as if winding up a clockwork toy.
...This looks remarkably low-tech.
Can a single wind of a spring really facilitate that many complex movements?
Just as I was harboring these skeptical thoughts, the spring was fully wound. With a sharp mechanical click, the doll began to stir.
"Would you care to test them?"
"I won't be held responsible if they end up in pieces."
"That is of no concern to me."
As Shutara Senjumaru stepped back, the two dolls assumed combat stances.
The moment I drew my blade, they lunged at me instantly.
'This speed... for a bipedal wind-up doll, isn't this a bit fast? Can that small amount of winding really produce this much kinetic energy?'
To observe their movements further, I refrained from attacking and focused solely on parrying their strikes.
As the dolls' blades clashed against mine, I couldn't help but be struck with awe.
'What in the world?'
It wasn't that they were exceptionally powerful, but the fact that they could move for this long off a few mere turns of a key was astounding.
Furthermore, their grip strength was high-tier. We must have exchanged twenty blows by now, yet their hold on their swords remained iron-clad. Type 1, in particular, despite wielding a heavy katana, moved with a grace only slightly inferior to a rank-and-file slayer who has mastered Breathing techniques.
Their physical strength was enough that they didn't give an inch even when our blades locked multiple times.
'What is the principle behind this? How did she build this? More importantly, how is it even functioning?'
More than that...
"However, compared to what you said, it doesn't seem like they're using that many different movements."
Despite the claim of many programmed actions, I grew suspicious as Type 0 repeated a three-pattern cycle, while Type 1 stuck to a seven-pattern cycle.
"That is because their actions are determined by the number of rotations given to their wrists and fingers. These are combat training puppets, designed for a puppeteer to manipulate their movements to strike at a swordsman's specific weaknesses."
True to Shutara-san's word, once she manipulated several joints on their hands, they began to move in entirely different patterns.
'How on earth did she manufacture this?'
Still, I could see why these couldn't be used for actual warfare.
The puppet and the master are like a two-legged race. While their speed, mobility, and stamina were far beyond expectation, their patterns remained limited unless someone was there to constantly recalibrate them.
Even if the sequence was randomized rather than linear, the ceiling of their potential was capped by the hard-coded patterns.
They might be able to handle a low-level Demon, but since Shutara-san is likely the only person capable of making dolls of this caliber, and there are no automated factories, mass production is out of the question.
Hmm... actually, if utilized correctly, could a dedicated combat automaton be possible?
"But... are these uniforms and Nichirin Blades the real deal?"
Isn't it inefficient to put genuine equipment on training dolls?
"Indeed. The blades are 'failures' that Master Nimaiya discarded, which I salvaged. As for the uniforms, I craft them myself."
"You make the uniforms yourself?"
"The Demon Slayer uniform is my invention. Tailoring a single suit is a trifle for me."
'Just what is this woman incapable of doing?'
***
In front of her, I demonstrated every form of Moon Breathing.
"Hmm... exceptionally swift. To replicate your movements, I shall need to add at least two more arms. And the number of designated actions must be vastly increased compared to my other puppets."
Shutara Senjumaru began sketching and writing furiously on a scroll with a brush.
It appeared she was recording the movements I had just showcased.
However, since she was only observing from the side rather than swinging a blade herself, a few minor errors appeared in her notes.
I didn't just stand by and watch.
"Regarding the Second Form: Pearl Flower Moongazing, it needs to be swung in a much broader arc than that."
"Was that form not intended to parry an opponent's attack?"
"Well, it can be used defensively, but it is fundamentally an offensive form. Why not combine both defensive and offensive action patterns? You said you were giving it extra arms anyway, right?"
I offered improvements whenever I spotted an error.
"Also, when using the First Form: Dark Moon, Evening Palace, it's better if the lead foot and the swinging arm are on the same side."
I added details regarding the posture and footwork of the swings.
"It might be interesting to add a behavior where it immediately follows up with the Fifth Form: Moon Spirit Calamitous Eddy after the Seventh Form: Mirror of Misfortune, Moonlit, to keep the opponent off balance."
I even suggested a few 'instant kill' combo patterns.
"How about adding a feint where it looks like it's initiating the First Form: Dark Moon, Evening Palace, but switches to the Third Form: Loathsome Moon, Chains?"
"That is a fine idea, but what of the Sixth Form: Perpetual Night, Lonely Moon - Incessant for a wider area of effect?"
"That's not bad either... but if you want the transition to be natural, the Third Form: Loathsome Moon, Chains would be easier since it's the same horizontal slash."
I added several feint attacks into the design.
Periodically, I would demonstrate the Moon Breathing forms again to help her refine the details.
"Oh, and to add to the sense of dread, let's give it six eyes."
"Now that is going a bit too far."
"What about barbed horns on its back?"
"What are you, some kind of Demon?"
Designating the action sequences alone took a full week.
"By doing so, we have reached 108 implementable movements. To execute all of these, I shall need to add not just two, but four extra arms. And your suggestion to construct it out of Black Scarlet Iron Sand—the primary material for Nichirin Blades—instead of wood... that is a truly fascinating idea. It has been a long time since I felt this inspired to show my true skill."
"I'm looking forward to it. How long do you expect the production to take?"
"Let's see... if I am fast, three years. If not, perhaps five."
That is an incredibly long time.
"And this is the reward I promised."
What she handed to me was...
"Clothing?"
It was a Demon Slayer uniform.
"A Hashira can receive as much salary as they desire, can they not? I decided it would be better to give you this rather than coin. I crafted it based on the measurements I took when you first arrived; it should be far more comfortable to move in than your current attire."
To match my purple Nichirin Blade, the uniform was a base of deep black on the outside with a stark white lining on the inside.
"I shall send a Kasugai Crow once the masterpiece is finished. I look forward to our next meeting."
Shutara-san gave a parting greeting and vanished into her workshop.
...I honestly don't know if a puppet that can perform all those movements can truly be made.
Even with 21st-century technology, that would be a tall order. Well, I suppose she'll compromise where necessary.
Unless...