Night soon fell.
By this time, Riezel had returned to his house and was sitting on the veranda, flipping through the old book containing records about Yoriichi Type Zero.
Surprisingly, the contents of this old book were extensive, thick with text and illustrations. Even Riezel couldn't finish reading all of it at once. Hence, he brought the book back with him and promised Kotetsu that once he finished reading it, he would help repair Yoriichi Type Zero.
Truthfully, the task wasn't difficult.
Once Riezel noted down the blueprint of Yoriichi Type Zero, he could directly use structure system magic to manufacture a new Yoriichi Type Zero.
Providing an old model with new components was a piece of cake then.
After confirming the internal mechanisms and positions of all the parts within Yoriichi Type Zero, Riezel could easily replace all the internal parts with new ones using his magic. A simple repair of its exterior would then revive this combat mechanical doll, restoring it to its former glory.
By the way, it seemed that Tanjirou still wanted to confront Yoriichi Type Zero. When Riezel planned to return home, he appeared to still be battling it.
Although Tanjirou briefly regained ground using Flame Breathing, he was still far from reaching the strength of a Hashira even with Sun Breathing, let alone the weaker Flame Breathing.
Of course, Kotetsu vehemently opposed this.
"Yoriichi Type Zero is almost broken, and you still want to fight it?! No way!"
After saying that, Kotetsu hurriedly took Yoriichi Type Zero back home.
However, Tanjirou's stubbornness refused to yield.
"Let me fight it one more time! Just once more! After this, I won't fight it anymore! I promise!"
In the end, as Tanjirou strongly insisted, he ended up following Kotetsu.
Knowing Tanjirou's temperament, he might very well still be dining with Kotetsu at this moment.
Riezel paid them no mind, focusing solely on bringing the old book back and diligently studying it. Whether or not he understood the contents, he meticulously remembered everything.
"Good, the blueprint is in this book."
At the end of the book, Riezel finally found the blueprint for Yoriichi Type Zero.
Surprisingly, this blueprint not only included illustrations but also detailed textual explanations. It meticulously described Yoriichi Type Zero's design principles, operational theories, and even set out one hundred and eight motion patterns for it.
From this, it was evident that Kotetsu's ancestor had devoted considerable care to Yoriichi Type Zero and sincerely hoped that his descendants could inherit his knowledge and ideals, thus advancing the art of mechanical doll crafting.
On the last page, it appeared that Kotetsu's ancestor had left behind a message.
—Without a doubt, the birth of Yoriichi Type Zero was a miracle, but its prototype, the swordsman revered as a god by everyone in the Demon Slayer Corps, was an even more incredible miracle. It makes one wonder involuntarily why such a character was born as a human and not as a god.
—Yoriichi Type Zero is undoubtedly the strongest and most outstanding mechanical doll in the world. However, it ultimately failed to fully replicate that swordsman's power. For someone like me who is determined to reproduce that swordsman's power in a mechanical doll, it can only be considered an unfinished product.
—Unfortunately, I no longer have time to continue researching and improving. I hope that future generations inheriting my knowledge will continuously refine this knowledge, allowing that swordsman's swordsmanship to reappear in this world.
From this message, Riezel could discern the writer's sighs, pride, and regrets.
'Recreating Tsugikuni Yoriichi's power with a mechanical doll?'
Riezel muttered inwardly, then chuckled.
'If it could really be done, the value of this legacy would probably increase by more than a thousandfold.'
As midnight approached, Riezel closed the old book he had been poring over.
He had completely memorized the contents of the book, whether it was the illustrations or the blueprint for Yoriichi Type Zero.
If Kotetsu found out about this, he would surely be astonished, wouldn't he?
Even an ordinary person couldn't finish reading through such a thick book in just a day, let alone memorize it. Yet, Riezel not only read it but also memorized it effortlessly in less than a day, almost inhuman.
It was thanks to his exceptional memory that he could effortlessly recall the entire contents of the book.
Now, when Riezel closed his eyes and thought back, the blueprint for Yoriichi Type Zero would appear before him, displaying every part and component on its surface and inside. As he deepened his comprehension of the blueprint, he carefully confirmed the positions, structures, and materials of each part, one after another.
After a while, Riezel extended his hand.
*Shing—*
Suddenly, a burst of light radiated in front of his palm.
It was a glow formed from magical energy.
Before long, the light transformed into a magic circle, flew out from his palm, and hovered above the ground like a scanner, moving upward.
As the magic circle pulsated, a mechanical doll slowly materialized and eventually took shape.
"It's done..."
Riezel opened his eyes and looked at the mechanical doll before him with a smile. What he saw was a mechanical doll that was truly identical to Yoriichi Type Zero.
He was certain that this mechanical doll was identical to Yoriichi Type Zero, both internally and externally.
The only difference was probably that it didn't need a key to activate.
Yoriichi Type Zero was activated with a single key and could change its combat mode based on the opponent's combat style by twisting its finger joints, thus being regarded as a combat training mechanical doll.
However, he felt that if every doll had to be activated with a key and needed a special method to adjust its action, it would be too troublesome.
For this reason, he removed these two functions.
Now, after removing them, how should the mechanical doll be activated, and how should its combat mode be adjusted to fit the situation?
It was simple.
"Contract."
Riezel extended his hand once more and pressed it against the mechanical doll's forehead, chanting a contract magic.
Indeed.
He formed a contract with the mechanical doll before him.
It wasn't an attendant contract, nor was it a slavery contract; it was a summoning and employing contract.
On the Akasha Continent, contract magic wasn't limited to just attendant and slavery contracts.
For instance, the contract magic Riezel was using now was commonly employed by control system magicians.
Control system magic referred to any magic capable of controlling and dominating external entities or concepts, including but not limited to summoning magic. Control system magicians proficient in summoning magic often used it to summon monsters or dolls and control them for combat purposes.
The summoning and employing contract was precisely the type of magic control system magicians used to control monsters or dolls. By imprinting contract marks on monsters or dolls, control system magicians could summon and employ these entities for combat purposes.
At this moment, Riezel was doing the same.
Once he imprinted the contract mark on the mechanical doll's forehead, Riezel withdrew his hand.
When one looked at the mechanical doll, a pattern resembling a magic circle was inscribed on its forehead.
"Come."
Riezel stepped back two paces and commanded the mechanical doll.
*Ka-Ka!*
Suddenly, the mechanical doll moved, obediently walking toward Riezel as ordered.
"Stop."
As Riezel issued another command, the mechanical doll immediately halted its steps.
"Turn left."
As Riezel gave a new instruction, the mechanical doll turned to the left without hesitation.
"Turn right."
"Move forward."
"Move backward."
"Stay in place."
When Riezel gave one command after another, the mechanical doll complied with all of them perfectly.
Seeing this, a smile appeared on Riezel's face.
'Isn't this much more flexible than Yoriichi Type Zero?'
Obviously.
Yoriichi Type Zero not only required a key to start but, once activated, it entered a pre-set combat mode and operated according to that mode—rigid and without flexibility.
If one didn't adjust the finger positions to change Yoriichi Type Zero's actions, it might even repeat its movements after completing the pre-set actions. As a result, anyone who had fought against it could gradually predict its movement trajectory and action patterns, provided they could persevere.
In the original work, Muichirou could eventually defeat Yoriichi Type Zero, possibly because of this reason.
However, this problem had been solved now.
The newly made mechanical doll no longer operated with a key and predetermined movements but was directly manipulated by its creator, Riezel, through contract magic.
With just a command from him, the mechanical doll could move and engage in combat accordingly.
'If I were to personally control this mechanical doll in battle, its combat effectiveness would probably increase significantly.'
Riezel circled around the mechanical doll while contemplating.
'Now that I think about it, maybe the parts and components on this mechanical doll could be replaced...'
Riezel intended to upgrade the materials on the mechanical doll's body, using metals with similar weight and properties.
Originally, the materials used for the mechanical doll were generally wood, with only the internal parts being metallic. If all these materials were improved, its performance would definitely increase.
As for which metal to use, Riezel needed to conduct thorough testing. Otherwise, if changing the weight or structure of the mechanical doll made its operation difficult and caused its performance to decrease rather than increase, it would be unfortunate.
'Well, there's still time, let's try it out slowly.'
At this moment, Riezel was like a child with a new toy, ready to thoroughly enjoy it—his smile never faded.
And so, the night passed in this manner.
===
The next day, early in the morning.
Riezel, still on the veranda of his house, looked as though he hadn't slept all night.
It was not without reason.
At this moment, he gazed at the figure before him and exhaled deeply.
"Finally done..."
A brand-new mechanical doll stood before Riezel.