Over 300 years ago, during the Sengoku era, Kotetsu's ancestor encountered a swordsman of the Demon Slayer Corps.
This swordsman possessed unparalleled skill; no matter how powerful the Demon, it could not withstand his single strike.
'If there were many swordsmen like him, the Demon Slayer Corps would not have to suffer so many deaths.' Kotetsu's ancestor conceived the idea of creating a combat-type Mechanical Doll based on this legendary swordsman.
After a long period of painstaking effort, Kotetsu's ancestor finally created a Mechanical Doll that captured some of the essence of that legendary swordsman. To reproduce the swordsman's techniques, the doll was given six arms, each holding a sword, capable of performing 108 movements.
Tragically, Kotetsu's ancestor passed away soon after completing the Mechanical Doll, without having the chance to pass on the complete method of construction to his descendants.
Thereafter, the Mechanical Doll was used by Demon Slayer Corps swordsmen for combat training. As time wore on, lacking proper maintenance, the doll gradually decayed.
By Kotetsu's generation, the accidental death of his father meant the complete loss of this unique skill's inheritance. The Mechanical Doll was nearly decommissioned, its use discontinued, and only a few older swordsmen remained aware of its existence.
Kotetsu, who had previously felt like a sinner of his family, now watched as the Mechanical Doll was completely brought back to life before his eyes.
"Is this a dream?"
Kotetsu harshly pinched Tanjiro's cheek, causing him to cry out in pain.
"So it's not a dream."
Kotetsu immediately dropped to the floor in a full prostration toward Aomori. "I kneel to you, Great Master! This boy was blind and failed to recognize a truly great man!"
"His attitude changed so fast!" Tanjiro rubbed his cheek, grumbling. "What if it still can't move?"
Slap!
Kotetsu smacked Tanjiro. "I am a Swordsmith from the Swordsmith Village! Do you think I can't tell the real quality of Kakado Great Master's work? Kakado Great Master is absolutely an old hand!"
'So he has this skill, too. He truly is a man of mystery,' Kanae thought silently.
Aomori finished patching up the doll's face, completing the final task. He clapped his hands and said, "Given the limitations of the era, creating a Mechanical Doll like this was already remarkable. I added a little something extra; let's see if it works."
"It definitely will!" Kotetsu had blind faith.
The group moved the Mechanical Doll to an open space outside the house. Kotetsu's hands trembled as he inserted the key, turning it a few times. After hearing a "click," he hastily ran away from the doll.
A few meters away, everyone held their breath, silently watching the Mechanical Doll, afraid to disturb it.
Click-clack-clack...
A few seconds later, the doll suddenly crouched down. Its six arms abruptly swung out, performing several beautiful sword dances.
"Eek! It moved! It moved! Hurray!" Kotetsu clapped his hands joyfully.
"Wow, that's so cool," Tanjiro was equally excited.
"That's wonderful," Kanae smiled, also clapping softly on the side.
With a thud, Kotetsu prostrated himself again. "I kneel before you once more, Great Master! You are amazing!"
Aomori smiled and said, "How about it? Want to learn? I'll teach you."
"Can I?" Kotetsu excitedly hugged Aomori's leg. "Great Master, I want to learn doll-making!"
"Hmm, later. I want to test it one more time." Aomori looked at Kanae. "Big Butterfly, can you do me a favor?"
"Big Butterfly?"
"That's right. You're the Big Butterfly, your sister is the Little Butterfly. Your whole family is butterflies, so we need to differentiate, right?"
"???" Tanjiro was full of question marks beside them.
'Your whole family are butterflies! Sister Butterfly, please scold him!'
"Is that so? That's a lovely nickname. Little Butterfly, haha ^_^, Shinobu's nickname is so cute too!" After imagining the scene, Kanae continued, "Kakado-san, you want me to test the Mechanical Doll's performance? I can do that."
"Exactly. You are the only one here who knows its original form. I appreciate the trouble."
Kotetsu activated the Mechanical Doll again. Aomori pulled Tanjiro back about ten meters. Taking advantage of the moment, he asked Tanjiro, "Doesn't the doll's face look familiar?"
Tanjiro blinked: "Huh? No, it doesn't."
"This Mechanical Doll is named 'Yoriichi Type Zero.' Its prototype is the Demon Slayer Corps swordsman, Yoriichi Tsugikuni, from over 300 years ago. Watch its movements closely."
"Oh." Tanjiro was still a little confused, but he widened his eyes to observe the movements of "Yoriichi Type Zero."
In the clearing, "Yoriichi Type Zero" started its attack. Six swords traced profound trajectories, simultaneously attacking Kanae.
Kanae's Flower Breathing is a derivative of Water Breathing, possessing its cutting power, while her flowery, brocade-like sword work also carries the ability to confuse enemies.
The confusing aspect was useless against the Mechanical Doll, so Kanae emphasized her speed to easily block "Yoriichi Type Zero"'s attacks.
But "Yoriichi Type Zero" did not stop. Six swords followed six swords; the offensive surged toward Kanae like a tide. Kanae, wearing a haori patterned with colorful butterflies, moved gracefully and swiftly, swaying left and right like a beautiful flower in the midst of a tidal wave.
'Compared to before, the attack speed is faster, and the transitions between techniques are much smoother. It's so much stronger.' The thought flashed through Kanae's mind.
She felt like she was fighting six swordsmen who were perfectly coordinated. Even with a physical constitution far superior to an average girl's, Kanae knew she couldn't maintain this for long.
'Then, I must use offense as defense!'
Kanae gradually immersed herself in the battle, as if fighting a Demon, adjusting her physical functions to their peak. She, too, had a competitive spirit!
Flower Breathing, Second Form: Honorable Shadow Plum!
She launched arching slashes in four directions, their trajectories resembling plum blossoms, deflecting all six swords.
Flower Breathing, Fifth Form: Peonies of Futility!
She delivered a nine-strike barrage from four directions, piercing toward the same point like peony petals. It struck the armor in front of "Yoriichi Type Zero," sending it flying.
Lying on the ground, "Yoriichi Type Zero" finally stopped moving.
"I won! Yay!" Kanae jumped up happily. When she landed, her purple eyes glanced at Aomori, turning into a little girl seeking praise.
"Not bad. Truly worthy of the Flower Hashira," Aomori complimented. "It seems trying to defeat a Hashira with a Mechanical Doll is still a bit too much."
"It's very strong, though. I used all my strength," Kanae said while adjusting her clothes and hair.
"What about you, Tanjiro?"
"Hmm, I feel like I've seen it somewhere, but I can't recall right now," Tanjiro shook his head.
"It's alright. Take your time to think."
Just then, a series of "grumbling" sounds broke the silence. Tanjiro clutched his stomach: "Ah, I'm hungry."
Of course. It was late in the night, and they hadn't eaten since noon.
Kanae chuckled. After the intense exercise, she was also a bit hungry.
"Then let's go back and eat."
Kotetsu was still checking the battle-worn "Yoriichi Type Zero" for damage. Aomori pulled him aside and whispered a few words to him.
As they said goodbye, Kotetsu seemed distracted, as if contemplating something.
On the way back to the Butterfly Mansion, Kanae asked curiously, "What did you say to Kotetsu in the end?"
"Nothing much. I just told him to study the Mechanical Doll and fully grasp its internal mechanisms. His family was unable to learn the core technology precisely because they treasured the doll too much and were unwilling to dismantle it," Aomori said flatly.
"Break before rebuilding, I see." Kanae sighed. "It's a shame few people have that kind of courage."
"That's how it is."
The return trip was uneventful. Back at the Butterfly Mansion, Kanae was subjected to a thorough scolding by Shinobu. It was then that Kanae introduced Aomori to Shinobu, of course, as Kakado, the Rumble Hashira.
After eating their fill, Tanjiro instantly fell asleep on the bed. Aomori, however, held the Breathing Style documents sent by Kagaya's subordinates and meticulously studied them by candlelight.
He intended to apply his knowledge by analogy, hoping to find a way to enhance his own Thunder Breathing and perhaps restore Sun Breathing.
The night deepened, but the candle remained lit.
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