After sleeping for roughly six hours, I woke to find the sun already high in the sky. I checked the blade I had made just in case, and fortunately, there was nothing wrong with it.
Then it was time to work on the hamon. To create the hamon, I first had to make yakibatsuchi mixed with charcoal.
Yakibatsuchi was a clay slurry made by mixing refractory clay with charcoal powder and whetstone powder. However, this was Orario, overflowing with magic stones. I used only about half the usual amount of whetstone powder, then finely ground a Flame Rock magic stone from the middle floors and mixed it in.
After mixing it thoroughly, a dark gray clay was complete. I applied it thickly along the spine for slower cooling and relatively thinly along the edge for rapid cooling. If the yakibatsuchi was not applied properly, the blade could warp during quenching, so I had to be careful.
I carefully secured the tang in the vise standing beside me. If it so much as shifted while I was applying the clay, that alone would be a disaster.
'All right, leave the hamon to me!'
...Sure. Go ahead.
'As you may remember, one of the greatest characteristics of the Sentō is its zigzag-pattern hamon. I also made the blade tip a kamasu-kissaki with a very shallow angle, just as you forged it.'
'When I made this one, I happened to see a fairly ancient katana and drew inspiration from it.'
'Anyway, the yakibatsuchi you made is fine, but from what I can see, you ought to add just a little more magic stone powder.'
'There is nothing particularly difficult about drawing that zigzag line. Apply the yakibatsuchi properly, then scrape it away veeeery thinly along the line. Once you have done that, well... it may be hard for you to accept, but your illusion will handle the rest.'
I'll apply it my way for now. Step in if you think it absolutely won't work.
'Got it, got it~'
I began by applying the yakibatsuchi. With a painting knife—the sort of tool people often called a palette knife—I gently spread the yakibatsuchi over the blade.
Swoosh.
Swoosh.
Swoosh.
Thick on the spine, thin along the edge.
By controlling the cooling rate during quenching this way, the edge cools rapidly, forming a martensitic structure and expanding in volume—martensite expands by 4.4% as it forms. Meanwhile, the spine cools slowly and forms a pearlitic structure. The difference in their cooling rates causes the edge to curve toward the spine, transforming the blade into a shape optimized for cutting.
In any case, trusting my senses, I loaded an appropriate amount onto the painting knife and applied it.
I coated the spine and edge to the required baseline thickness, taking care with the layers. What I applied after that would be for drawing out the hamon. From here on, I truly had to pour my heart into it.
...There was one method.
Is it possible?
'Hmm... if you intend to do this without relying on the illusion... then this is probably the method with the highest chance of success available to you. But the difficulty will become insane.'
That doesn't matter. I have made countless high-difficulty weapons.
'I like that confidence. Give it a try!'
The principle behind a hamon was the difference in cooling speed between the coated and uncoated portions, caused by partial heating with yakibatsuchi. Then what if, instead of drawing lines to outline the pattern, I drew a single line directly on the edge with yakibatsuchi from the start?
It was an extremely difficult task, one that tolerated not even the smallest mistake. I had to draw a line that could not have been more than a millimeter thick, repeatedly maintaining the same pattern in clay.
I took a long, thin strip of bamboo, dipped it into the jar of yakibatsuchi, and pulled it out.
Then... I begin.
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How much time had passed? I concentrated and concentrated, until all I could see was the zigzag line being drawn across the blade before my eyes.
Who I was and what I had been doing meant nothing. There was only one thing here that held any meaning.
Finishing this line.
Continue.
Continue.
Continue.
The single line that began at the gently curving tip was finally approaching its end.
After reaching that end, Smith remained perfectly still for a while. Only after about five minutes did he come back to himself, stretching and twisting the body that had stiffened from working in the same posture for so long.
Crack.
Crack-crack-crack.
Crunch.
Several sounds that should never have come from a living body rang out, but there was no problem.
What time was it...? Roughly six hours had passed. I finished earlier than I expected.
For heat treatment, the yakibatsuchi needed to harden while drying for about half a day to a full day. I filled my stomach with the jerky and water I had stockpiled, then went back to sleep. This time, my mind was truly exhausted.
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...I had a dream. In it, a blacksmith held a sword made entirely of black and swung it around, testing whether it had turned out well.
'Right, your name is...'
Then I woke up. The sun was rising again. My sense of time was starting to feel strange. Every time I opened my eyes, I was looking at the morning sun...
That dream just now... was probably this guy.
'Yeah? What is it?'
...Nothing. Now I need to heat it in the forge... This is the trickiest stage for a Japanese sword.
If the blade temperature went too far above 800 degrees, it would fail. If it was too far below 800 degrees, it would fail too. Of course, the material was orichalcum rather than tamahagane, so there should be some leeway... but temperature control was difficult all the same.
Before beginning, I prepared clean spring water I had drawn from a mountain near Orario as the cold water for quenching. Since coming to Orario, I had mostly used oil quenching, but in the East, water quenching rather than oil quenching was more common.
I poured the spring water, which I had kept cold by burying its jar in the ground, into a rectangular quenching tank. To observe the blade's changes in temperature during this process, I had to make the workshop as dark as possible, so I shut the windows and even put up wooden boards to block out the light. Now, all I could see was the blazing fire in the forge.
Preparation was complete. It was time to heat the blade in the forge.
This time, rather than use the magic-stone bellows, I intended to control the fire myself with the bellows.
Here I go...
Holding the blade in my hand, I pressed it into the charcoal in the forge until it was slightly buried, then gently worked the bellows with my foot and gradually raised the temperature.
Whoosh.
Whoooosh.
Fwoosh.
Working the bellows gently, I slowly increased the temperature of the forge. By my estimate, I should pull it out at around 900 degrees. Is that right?
'Hmm... considering the properties of the material, that might be enough?'
All right. Thanks.
'Don't mention it! I exist for the completion of the Sentō!'
I half-listened to Shikizaki Kiki while periodically pulling the blade out to check its temperature, flipping it over each time to avoid the unfortunate possibility that heat might not be spreading evenly through it.
600 degrees...
700 degrees...
750 degrees...
800 degrees...
900 degrees...!
The moment I pulled it out again and confirmed it was roughly 900 degrees, I plunged it straight into the quenching tank beside me, edge first.
Sssssssssss...!
A familiar sound reached my ears. These days, everyone in Orario used oil quenching, and I had grown more accustomed to the sound of burning flames. But when I worked at home in my previous life, I generally quenched in water, so it had been a very long time since I heard the sound of water evaporating. I had liked the heat rising with the steam, too, though it was a little disappointing that ordinary heat no longer registered for me at all.
I lifted it out once to check for warping, then quenched it again, edge first.
Ssssss...
The sound of evaporation was slightly more subdued than the first time.
Once I felt it had cooled sufficiently, I left it submerged and wiped the yakibatsuchi off the blade with a cloth-wrapped stick. Examining it as I cleaned, I could not yet see the hamon because the edge had not been polished, but there did not seem to be any warping or cracks.
I could not be certain until I polished it, but the blade itself seemed like it would be fine.
Even after heat treatment and quenching, work remained. If I left it like this, the blade's hardness would be too high and it would become brittle, so I had to temper it at an appropriate temperature.
I put the blade back into the forge, which had not yet cooled, heated it again, and took it out. Now I simply had to let it air-cool.
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After some time had passed, I flicked the blade with my fingernail, and a clear note rang out. Fortunately, its toughness seemed to have improved. I probably did not have to worry about it being so hard that it would break easily.
From here onward, it was time to concentrate again.
Using 2,000-grit, 5,000-grit, and 9,000-grit whetstones in order, I slowly sharpened the edge.
There was no need to hurry. I emptied my mind and repeatedly pushed and pulled the blade, imagining another form hidden within it.
Shhhhk.
Shhhhk.
Shhhhk.
Shhhhk.
Shhhhk.
Shhhhk.
The sound of the whetstone filled the forge like the sound of waves.
With every push and pull, I injected illusion into it. The image rising in my mind this time was a syringe. One piston stroke repeated with each back-and-forth motion. As the hamon emerged, the illusion slowly began spreading over the entire blade.
Though it had been made from orichalcum that should have been pure white, the darkened blade now gleamed entirely black. Along its edge, a zigzag hamon—the very symbol of the Sentō—revealed itself, accompanied by an eerie violet glow.
'Even seeing it again, it is beautiful.'
Yeah... what a killer sword.
Now it was time to make the habaki. Even before the edge was complete, I could have roughly carved the wooden portions of the scabbard and handle beforehand. But if I used a pre-made habaki, there was a risk it would not fit securely and would rattle, so I intended to make it to match the finished blade.
I took out a piece of brass, put it into the forge, and removed it as soon as it heated up. Then I took the rectangular brass piece and lightly tapped it with a small hammer.
As I struck it while pouring in illusion, the brass began turning black...? What the hell? This was not some kind of chaos infusion, so why was it being dyed?
'It seems to have turned black to match the fact that every part of the Sentō is black.'
...Anyway, once it had spread out to an appropriate width, I held it against the lower part of the blade and slowly folded it into place, fitting it as tightly as possible without putting too much shock into the blade.
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By the time I finished the habaki, night was approaching once again. The habaki had not been visible at all in the anime, but it could not possibly have had no habaki at all, so I made an extremely short one, barely a centimeter long, and fitted it on.
After that, everything proceeded smoothly. The tsuba, the guard, and the seppa, the fittings placed above and below it, had been prepared in advance since using pre-made pieces for those would not cause much trouble. Still, the tsuba had an unusual diamond shape, with an inverted triangular pattern engraved along its side, so I checked it one last time.
Fortunately, the Raider Fish skin Kaguya had brought had a texture similar to stingray skin, so it looked like I could make a fine piece. I held the two sides of the tsuka, which I had already carved into a concave, gourd-like shape while fitting them over the tang, against it.
Fortunately, they fit perfectly, without any protruding or misaligned parts. Even when I gripped the assembled tsuka and turned it upside down, it did not move in the slightest.
Fortunately, the Sentō did not have much that could be called flashy ornamentation—the hamon and tsuba were the most extravagant parts—so I did not need to make decorative pieces.
First, I fitted the tsuka, wrapped in Raider Fish skin coated with adhesive, onto the tang and drilled the hole for the mekugi peg. In Japan in my previous life, swords had become a kind of collector's hobby item, so bamboo or horn pegs were used to make them easy to disassemble and reassemble. But this was Orario, a place where battles with monsters or people happened constantly. For stability, I intended to use a steel mekugi.
I removed the blade from the tsuka again and tied the tsuka-ito around the handle. I used cotton thread made from cotton trees grown from a variety said to have been brought from the Far East. The knotting method was so complex that, even with Shikizaki's advice, I failed several times before tying it together, however clumsily. Then I disliked how sloppy it looked and repeatedly untied and retied it. It might have been more difficult because the tsuka-ito was tied in an inverted triangular pattern rather than the diamond pattern I knew.
Once I had fitted the remaining small ornaments and metal components, things became comparatively easy.
The habaki was already fitted on the blade, so I checked the completed tsuka one more time for anything strange, then slid on the seppa, tsuba, and another seppa in that order before finally attaching the finished tsuka. It felt as though they had always been one piece, with no sense of incongruity whatsoever.
Normally, it should have been secured by driving in a bamboo or horn mekugi peg, but to improve durability, I drove in a steel peg and fixed the blade and tsuka together.
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...Beautiful.
The sleekly curved black blade radiated a sharpness that seemed capable of cutting anything. Reducing a tachi into a kodachi had lowered the reproduction rate considerably, so it could not boast the sharpness of a monomolecular cutter. But the catch was that this weapon was not truly complete yet. Only after I finished the scabbard and the 'final task,' once illusion permeated it, would it be truly complete. Then I would finally see its true sharpness.
When I gave it a practice swing, it made a sound like it was cutting the wind. Even I, with no talent for swordsmanship, could produce that sound while wielding this incomplete blade. If Kaguya, who would be second to none in Orario, used it...
In any case, it was time to make the scabbard, the final task. The wood I would use was magical timber from Wyshe Forest, the same wood I had used before to make Finn's spear. I took two long pieces of wood, each cut to roughly seventy centimeters, and spent a long time carving them while repeatedly fitting the Sentō against them. Before I knew it, I could join the two pieces, insert the Sentō inside, and find no spots catching on it or scratches inside when I opened it again.
In Katanagatari, it never showed a sageo, the cord used to hang a Japanese sword from one's waist, so I did not make an attachment for a sageo. Still, I carved the scabbard with a kurikata, the fitting used to hang it from the waist, in mind.
After hollowing out the inside, it was time to carve the exterior in detail. Normally, I would have used glutinous rice paste as adhesive, but while ordinary rice was available, glutinous rice had not reached Orario yet. With a heavy heart, I joined it with wood glue instead. After carving it smooth enough that nothing caught when I ran my hand over it, I gently shaped the mouth and lower end of the scabbard again.
I carved two small pieces from a Minotaur horn I had prepared and slowly sanded them down. I shaped the lower piece first and fitted it onto the bottom; fortunately, it went in neatly without misalignment. Next, I used a chisel to make a hole in the horn piece for the mouth, then filed down each protruding part one by one while fitting it against the scabbard opening. Once the mouthpiece was complete, I applied adhesive again and carefully fitted it into place.
Now all that remained was to lacquer it and let it dry; then it would truly be finished... I took sap imported from lacquer trees in the Far Eastern mainland, picked up a brush, and slowly spread it over the entire scabbard. Luckily, I was not prone to lacquer rash. Otherwise, I might have had to leave the final scabbard work to someone else.
Leaving the scabbard gleaming with a glossy black sheen, I returned to the workshop and fell asleep once more...
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Five days passed after that. I controlled the humidity in the forge and kept the furnace going, applying lacquer once a day, drying it for a day in the furnace's heat, then applying another coat. After six coats in total, the Sentō's scabbard was complete, black as the night sky just like it was in the original work.
I could feel it. My magic recognized that this thing was complete and was preparing to trigger the illusion one last time.
'Wow, congratulations! Except for the length, it is exactly the same as the Sentō I made! Is it finished now?'
...Yes, it is finished. Once I complete the final task.
'Final task?'
Without answering, I silently stared at [Sentō Namakura] resting on the table, then gripped the hammer hanging at my waist.
'...? What are you about to do?'
Ignoring him, I raised the hammer above my head.
'Hey, hey! What the hell are you doing?! Why are you trying to destroy such a masterpiece yourself?!'
I continued to ignore him, filling the hammer with forging and illusion before bringing it down on [Sentō Namakura].
It looked as though it would shatter at any moment, but the sword was not what broke. Or rather, could this even be called breaking? More precisely, what dispersed was a black mist faintly tinged with green, spreading out the instant the hammer touched [Sentō Namakura]. I had undoubtedly swung with all my strength, yet at the instant it made contact with [Sentō Namakura], it was as if I had struck something else located in the same place; only the black mist scattered, not the sword.
'...Since when did you know?'
From the start. How much do you think I watched Katanagatari? I had been wary of your [Poison] from the beginning.
'Ha... What a shame.'
And when I acknowledged that this weapon was truly complete, I felt the illusion residing within [Sentō Namakura] tremble ominously. At the same time, the thought-form of Shikizaki Kiki began to fade as well.
'What a shame... If I had been lucky, I might have found a body with matching wavelengths and begun life once more...'
Get lost... And regardless, thank you.
'Ah... Keep working hard from here on out, young blacksmith.'
He left only those words behind and vanished. Seriously... I never thought that at twenty-nine, someone other than the gods would call me young. Anyway... I had really finished it.
For now, sleep... With that final thought, my consciousness went dark in the bed of my workshop.