What Akira said made everyone freeze in shock.
If they could actually make it, if they really could recreate Yoriichi Type Zero, then they could build an entire army capable of fighting demons without sacrificing human lives. But how?
Kotetsu shook his head immediately.
"That's impossible!"
Akira tilted his head. "Why?"
Kotetsu pointed at the Yoriichi Type Zero like it was some sacred relic. "This machine doll was made during the Sengoku period! It's like three hundred years old! The technology used to create it is already lost!"
Akira replied calmly, "Not really. I can find out how it was made using reverse engineering. And I've seen far more complex machines. I'm pretty sure I can make this."
Kotetsu shouted, "But how are you going to make it fight demons? It can't actively target or adapt to demon movements and powers! And what about Blood Demon Arts?!"
Akira answered simply, "Well, that's because it doesn't have a brain yet. But I just know how to do it."
Everyone stared.
What do you mean, brain?! You can make it?!
Their expressions said everything.
But Erika, who already sensed what Akira was planning, grabbed him immediately.
"Excuse me, I need to have a word with him."
She dragged Akira away from the group.
Once they were far enough from the others, Erika crossed her arms and glared at Akira.
"What are you thinking? Are you actually going to make a robot?"
Akira replied casually, as if she'd asked him about the weather.
"Technically, yes."
Erika's eyes widened. "How? Didn't Selena say we can't use modern technology here?"
Akira raised a finger. "I can't use modern tech we brought with us in our inventory. But if I create something from scratch, with materials from this era… then it counts as technology of this world, right?"
Selena's voice echoed telepathically through their minds.
"That's true. If you create it using only the tech of this era, it's acceptable."
Erika stared at Akira, incredulous. "But can you even make a robot in the Taishō era?"
Akira shrugged. "If Senku can do it with stone-age technology, I can do it too."
Erika blinked. "…Who is Senku?"
"An anime character," Akira said immediately. "But that's not important. What's important is that I can make them."
Erika exhaled. "And what about the time limit?"
Akira nodded. "Sure, I'd need more time if I were alone. But with the Ubuyashiki family's support and the entire swordsmith village helping, we can do it."
Erika frowned deeper. "That's assuming we can convince them. How are we going to do that?"
Akira smiled like it was the easiest thing in the world.
"Well, we can just ask, right? I don't think they'll reject it without hearing us out."
Erika sighed deeply, rubbing her forehead.
"Fine. We'll talk to them."
They returned to Tanjiro, Mitsuri, and Kotetsu to announce their plan.
Tanjiro tilted his head anxiously.
"Then… should I stop my training with this?"
Akira shook his head. "No, you can continue. Even if you break it or something, I'm pretty sure I can fix it or recreate it."
Kotetsu froze.
"Wh–WHAT DO YOU MEAN BREAK IT…?!" he screamed, his voice cracking.
Akira simply waved his hand dismissively, already walking away with Erika.
"Okay then, see you later."
"DON'T IGNORE MEEEE….!!" Kotetsu wailed behind them, but he was completely ignored.
Inside the village chief's house, Akira requested an emergency meeting.
The chief expected something about forging…
He did not expect this.
"So… you want to create more Yoriichi Type Zero units and make an army of machine dolls to fight demons?" the chief asked in a stunned voice. Even with the mask, his confusion was obvious.
"Exactly," Akira said.
The chief exhaled sharply. "That Yoriichi Type Zero was created over 300 years ago, during the Sengoku period. Not a single swordsmith has been able to reproduce it since. How are we supposed to believe you can do it?"
Akira answered calmly. "Reverse engineering. I've seen far more complex machines. I can figure it out."
The chief leaned forward, crossing his arms.
"Even if you could make one… how will it fight a demon? It can't use breathing techniques. It can't adapt to Blood Demon Arts. And a machine doll doesn't have a mind."
Akira smiled faintly. "Don't worry about its mind. I can make it. All I need is manpower and materials."
Tecchin's mask twitched. "We can't make this a priority easily. I need permission from headquarters, too."
"Then how about this?" Akira offered. "Give me a week or two. I just need some manpower and materials. I'll create one prototype. After you see it, you can decide what to do."
The chief fell silent, thinking hard.
Even the other masked smiths behind him were listening intensely.
Finally, Tecchin nodded.
"Fine. I'll give you two weeks. If you can create a working one within that time… we will discuss making more."
Akira grinned. "Deal."
They ironed out a few more logistics, materials, workspace access, and supplies.
Then Akira casually added:
"Oh, by the way. If I'm going to stay here long-term, I need a place to work. Can I build myself a house on the mountains?"
Everyone, including Erika, froze.
All had the same question. "What?!"
As they walked back to where the clearing was, Erika finally asked, "What do you mean you want to build a house in the mountains?"
Akira answered casually, "Exactly. I can't conduct my experiments inside the village, right? What if I blow it up or something?"
Erika looked at him in shock. "What are you going to do that's going to blow it up?"
Akira said, "It isn't dangerous or anything, but we can't be too cautious, right?"
Erika frowned. "But you said you are going to build it today or something. How are we going to do that?"
Akira replied as if it was obvious. "Didn't we used to build huge things in my backyard when we were children?"
Erika puffed her cheeks slightly. "You mostly did. I just cheered you on and played with you when you finished. And you used magic to build all those stuffs."
Akira nodded. "We can still use limited magics, right? The ones our Devices allow. My evolution powers and your gravity powers, I'm pretty sure we can build a house in a day."
Erika raised an eyebrow. "Fine, then where will we build it?"
Akira said, "We have to find a place. But we need help to find a perfect place."
Then they went to the clearing where Tanjiro was still training with Yoriichi Type Zero and Kotetsu. Mitsuri seemed to have gone away, probably because she had work or something. Akira explained their discussion to them, and then he asked Tanjiro for help finding a place to build his house.
As Tanjiro walked with them toward the mountain, he asked, "Akira-san, are you really sure they can be found?"
Akira nodded confidently. "Hot spring veins already exist in these regions. We just need to find an unused one. Can you find it?"
Yes, Akira was trying to find a hot spring for himself and build a house above it.
Tanjiro said, "I should be able to find it, but this entire place smells like a hot spring, so it's harder to locate one."
Akira replied, "Just think of where you smell them the most. You can probably find it."
They followed Tanjiro's nose, and soon they stopped. Tanjiro inhaled deeply, his eyes widening.
"I smell warm water! And minerals… coming from down there!" he said, pointing toward a slope covered in thick roots.
Akira smiled. "Perfect. Erika, now it's your turn. Use your ribbons to dig into the ground to see if you can find a hot spring."
Erika sighed and nodded. She summoned her Device, and her ribbons drilled into the earth. After a moment, Erika said, "Yes, I found hot water."
Akira said, "Good. Now, can you dig a hole to it?"
Erika glared. "Do you think I'm a mole?"
Akira replied, "I mean… your Device power is concept Earth, right? You should be able to do it."
Erika said, "I never tried doing earth-based powers before, aside from gravity."
Akira nodded. "Well, you have to learn it sometime, so now is the best time. You dig us a hot spring, I'll build a house."
Erika sighed. "I'll try."
Selena's voice chimed in telepathically, "Don't worry, Erika-chan. I will help you master Earth magic".
Akira turned to Tanjiro. "Thank you for your help, Tanjiro. We'll carry on from here."
Tanjiro said, "No worries, Akira-san. But… can you two really build a house in a day?"
Akira answered casually, "Well, we can do magic, so it won't be too much of a problem."
So Akira and Erika said goodbye to Tanjiro and decided to build their house here. Somehow.
Akira stepped away to think about how to create his house. Several ideas passed through his mind, but he settled on a tree house, a house literally inside a tree. He knew that with his evolution ability, he could grow a tree that was hollow on the inside, forming a natural inner space like a wooden tower.
He retrieved a seed from his inventory. A keyaki tree seed.
He decided to use it.
Akira summoned his armor. Holding the seed in his palm, he whispered:
"Rewrite."
Instantly, the world shifted. Puzzle lines appeared across the seed, the blueprints, the DNA structure of the organism. When he used Rewrite, he always saw these lines. To modify the seed, he simply had to remove or increase certain puzzle lines, amplifying or weakening specific traits.
He was rewriting its structure through induced evolution.
He needed the tree to grow hollow. He needed natural floors, nodes spaced out along the inner walls. He needed the roots to grow beside the hot spring, not over it.
So he edited the apical meristem, cambium layers, and root meristems.
He altered growth pathways, redirected nutrient flows, reinforced lignin production, and introduced an entirely new internal blueprint:
A hollow trunk, with internal nodes every three meters.
A modified root network.
When he finally finished rewriting the seed, he opened his eyes. He wasn't sure how much time had passed, minutes or even hours, but Erika was still concentrating intensely, her ribbons tunneling deep into the earth.
Then suddenly, Akira felt a pulse of magic.
He instantly looked toward Erika.
A domain was forming around her.
The ground in front of her, where the hot spring should be, began to rise into the air as if gravity itself had reversed. Soil floated. Stones hovered. Then the entire mass shifted aside, revealing the hot spring beneath.
Akira asked telepathically, "Sister, what is that?"
Selena's voice came excited and proud. "That's her first Noble Art — Terra Gravitas. I named it myself! It's basically a domain where she can control the ground around her by anchoring her ribbons into the earth. For now, she needs them planted to use it… but I believe she'll be able to do it without them in the future".
Akira said, "That's awesome… but I can't believe she had a Device Reconstruction before she even made her first Noble Art?"
Selena replied, "Sometimes it happens".
Erika, still focused on her work, finally opened her eyes as the hot spring was completely cleared.
Akira smiled. "Good job. That was cool."
Erika, a bit tired, replied, "Whatever… I already did what you asked. So, did you finish the house?"
Akira grinned. "Hehe, let me show you."
He held out a small seed.
"This is our house."
Erika blinked. "…What?"
"I'll show you."
Akira planted the seed into the soil and activated it.
In an instant, the seed sprouted, roots burst outward, the trunk thickened, branches unfurled, and a giant tree grew right before their eyes.
Akira pointed proudly. "This is our house."
Erika stared. "…It's a tree."
"Yes," Akira said confidently, "but it's hollow inside. We can carve a house in there."
Erika crossed her arms. "…How are you going to make a kitchen? A bathroom? Lighting? Electricity? All the other things a house needs?"
Akira paused. "Well… we'll figure it out."
But in the end, they couldn't figure it out as Akira seemed to have overestimated himself.
Because it took two full days, with help from the villagers and his magic, to finish the house.
However, in the end, they managed to do it somehow.