Deep inside the freshly carved forge room of the living tree house, sparks crackled like fireflies gone wild.
CLANG.
CLANG.
CLANG!!
Akira hammered metal with the intensity of a man attempting to recreate civilization from scratch.
But he wasn't really recreating civilization like Senku, and this was still Taishō era, so the technology available wasn't that primitive. It definitely sped up the process of whatever monstrosity he was currently making.
After finishing construction of the house and adjusting all its interiors and exteriors, Akira had declared, "I shall turn one floor into a forge and workshop!"
Erika had immediately shut that down. "How the hell are you going to create a forge inside a tree?!"
Even after Akira claimed the tree was highly flame-resistant, she refused.
So they had to compromise.
They dug a chamber through the ground next to the hot spring to create a forge. Luckily, the tree house was close enough that the underground structure was practically connected.
And once it was ready, Akira dove headfirst into work.
The rhythmic pounding echoed through the wooden interior until soft footsteps approached.
"Akira? It's getting late." Erika's voice came from above. "What exactly are you still doing in here?"
But Akira didn't reply. He was completely absorbed in his work.
Seeing there was no response, Erika stepped into the forge, only to freeze.
Akira was intensely hammering something shaped like a mask… no, a helmet.
She walked closer. "What are you doing?"
Akira finally noticed her. "Oh, Erika. I'm just doing some finishing touches to this. It's already finished."
Erika frowned. "What are you making?"
"Hehe, let me show you."
Akira lifted the helmet, walked to the corner, and grabbed a sheet covering something massive. With a dramatic yank.
FWIP!
There it was.
A large armored body stood before them. When Akira placed the helmet onto its head, the shape suddenly became familiar to Erika.
It looked exactly like Iron Man's armor.
Specifically, the Mark 1 armor Tony built in the cave.
Akira spread his arms proudly.
"Behold. My latest creation. Solar-Powered Mobile Armor Unit Number One."
Erika stared.
Silence.
Long, painful silence.
Then she said, "…Akira."
Akira tilted his head innocently. "Hm?"
"Weren't you supposed to be making the Yoriichi Type Zero prototype?"
A single cold bead of sweat rolled down Akira's cheek. His smile froze. His eyes slowly widened in dawning horror.
"…Ah."
"You forgot, didn't you?" Erika leaned forward slowly.
Akira lowered the hammer. Very, very slowly.
"…Possibly."
Erika pointed at the Iron Man, looking at the armor in utter disbelief.
"How do you go from 'robot with six arms'… to Iron Man armor?!"
Akira looked at the armor.
Then at her.
Then at the armor again.
"…Creative detour."
Erika snapped.
"This is not a detour. This is several kilometers off the road, across a river, through a forest, and into another country! How in the hell did it even come to this?!"
Akira scratched his cheek. "Well… I don't know either. I just picked up the hammer, and the next thing I know, I just created it. I mean, it looked cool, and I always wanted to make one too. And I'm pretty sure it'll become useful one day, right?"
"Didn't you already have a magic armor?" Erika jabbed a finger at his chest. "When are you even going to use this?!"
Akira paused, realization hitting him like a falling log.
"…Hmm. Maybe not me, but someone else? Maybe?"
Erika inhaled deeply and then turned to the sky in despair.
"Selena. Why didn't you stop him?"
Selena's voice echoed telepathically in both their heads, sounding unapologetic.
"I'm sorry, I'm kinda busy myself, so I didn't notice what he was making".
Akira looked horrified. "Sister, you're actually doing something?"
Selena snapped back instantly. "What do you think? I do nothing but watch you all day or something?"
"…Yeah?" Akira answered honestly.
"Oh COME ON", Selena groaned. "I work too, you know".
Akira asked, "Like what?"
"Like I am currently working on adding a store function to the system", Selena replied proudly.
Akira's eyes sparkled. "Really? How does it work?"
"Well, I connected it to…"
"Can both of you NOT get distracted for like a minute and LISTEN to me?" Erika cut in sharply.
Both Akira and Selena immediately straightened.
"Yes ma'am."
Erika rubbed her forehead and continued, "Akira, you're supposed to be making a robot. But now you just made an armor for some reason. How are you going to complete the Yoriichi Type Zero now?"
Akira shrugged. "Well, we still have a week left. I'm sure I can make it."
"How?" Erika demanded.
"Well," Akira said, brightening, "I already made the power source, so that's one part complete."
Erika narrowed her eyes. "What's the power source?"
Akira explained. "It's solar-powered. I made a new solar reactor using scarlet iron the same ore Nichirin swords are made of as the core. Since they're highly conductive to solar energy, they make a powerful reactor. A full day charge can probably last for a while."
Erika raised an eyebrow. "So how are you going to make the CPU and other things?"
"Don't worry," Akira said with full confidence, "I already made the plans for it on the first day. I'm sure I can finish it. Somehow."
Erika exhaled the way someone does when they accept a future headache is inevitable.
"Just don't get distracted. And finish it before you make anything else."
"Yes, ma'am," Akira said obediently.
"Selena, look what he's doing too," Erika added sharply.
Yes, ma'am, Selena echoed telepathically.
"Good. Just finish it soon," Erika sighed. "It's already evening. I'll try to make some food."
With that, she left the forge, leaving Akira alone with his tools and the half-finished mess of ideas he'd created.
Akira slumped onto a stool.
"Well… seems like I have to plan these things all over again."
He grabbed a notebook and began scribbling furiously, design drafts, gear layouts, solar intake ratios, movement joints, potential problems, and solutions. He muttered to himself the whole time.
"I won't get distracted… I won't get distracted… not this time… definitely not this time…"
By the time he finished writing out the full plan for creating the Yoriichi Type Zero prototype within one week, he finally looked up and realized. "…Time passed already?"
He let out a tired sigh.
A hot bath would be perfect right now.
Akira stood, stretched, and made his way toward the underground bath area carved beside the forge. He was really glad he built the house above a hot spring, as it meant he could use it whenever he wanted. And since the forge was also underground, the bath and spring were just a few steps away.
"Perfect time for a bath," he muttered, stripping off his clothes and getting ready for the bath.
Then he slid open the door to the spring, steam billowing out around him, and stepped inside, still lost in deep thought about gear ratios, artificial brains, and CPU alternatives.
He reached the edge of the water, stretched his arms, and stepped in with a relaxed sigh.
"Perfect temperature… I needed this."
Only then did Akira realize something and froze.
Slowly… very slowly… he turned his head.
And there she was.
Erika. In the hot spring. Right there.
For a lifelong anime fan, this was exactly the kind of situation every protagonist was warned about. But Erika always locked the door. Always.
So why was it open today?!
Akira's brain stalled. He knew he should say something to salvage the situation, anything.
But he froze like a glitching NPC.
Erika, hearing the movement, turned her head.
And she froze, too.
Her face turned so red that she could be classified as a tomato-breathing technique user.
Then, without thinking, her gaze flicked downward.
And her soul visibly left her body.
And yes, Akira also noticed the problem.
Something was rising.
And it was definitely not the Shield Hero.
Akira choked out, "E-Erika wait, I can exp….!"
He didn't get to finish.
"GET OUT, YOU IDIOT!!!"
BAM!
Her fist connected with his face so hard he flew backward through the steam, slammed into the doorway, and vanished into the dressing room like an exorcised spirit.
"I'M SORRY!!" he screamed mid-flight.
Erika collapsed back into the water, burying her burning face in her hands, completely overwhelmed by what she saw.
Selena's laughter erupted in her mind. "HAHAHAHA! Even funnier than I imagined!"
"SELENA!!" Erika shrieked in her mind. "Why didn't you warn us!?"
"Well", Selena giggled, "I wanted to see that anime-like event happen in real life. Watching you two is my entertainment, after all".
"WHAT IS WRONG WITH YOU!?"
"Come on, Erika-Chan, if I interfere too much, it won't be fun anymore, right?"
"SELENAAAAA!!!"
The incident, unsurprisingly, left both Akira and Erika completely embarrassed.
They couldn't even look each other in the eye that night.
Erika didn't drink his blood either, which was very unusual for her.
Normally, Akira was someone who could just walk off anything. He had survived battles, getting lost in the void, monsters, and even the trauma of getting killed too many times, so he confidently assumed he could just walk off this, too.
He was wrong.
Because the rising of the Shield Hero had happened, and now he found himself… a little conscious of Erika, too.
This was his first time in such a situation, after all.
Still, he was Akira.
So after a day, he somehow forced himself back to normal.
Seeing him return to normal, Erika also managed to regain her composure, well, as normal as the situation allowed.
Though both pretended nothing happened, the event lingered in their minds.
And Akira realized… something inside him had changed.
But he shoved it aside and decided to think about it later.
He had a machine to build.
The creation of the new Yoriichi Type Zero prototype went surprisingly well.
Akira had already designed it, so he just needed to assemble it.
Of course, it ended up being a bit different from the original Type Zero.
Speaking of the original, Tanjiro somehow managed to break its face, exactly like in the anime.
And just like in the anime, Haganezuka immediately took it away to restore it for him.
It simply happened a few months earlier in this timeline, and since Muichiro hadn't arrived at the Swordsmith Village yet, he never got involved.
Things were shifting away from the anime more and more because of Akira.
But Akira didn't have time to dwell on that. He would think about what to do with Muichiro later.
Right now, he had to finish this new Yoriichi Type Zero.
He chose to reuse the solar reactor he created for the Iron Man–looking armor earlier.
But he also added a wing-like structure, thin plates made from scarlet iron, designed to act as solar panels to constantly recharge the machine.
The limbs, joints, outer plating, almost everything, was constructed with pure scarlet iron ore, giving the prototype incredible durability.
It still had six arms, of course.
As for the CPU…
it was mostly analog.
Akira had to manually connect gears, circuits, and tiny mechanical linkages to a special sensor he invented, one capable of detecting the presence of a demon.
He had to thank Nezuko for helping him test that part.
But because it relied on analog mechanisms rather than compact digital circuits, the machine's internal structure needed far more space.
So the entire prototype ended up growing to about seven feet tall.
And since he hadn't made a human-like face or outer shell, it looked more like a metallic skeleton with six arms attached.
But after working tirelessly for several days, Akira somehow managed to finish building it right on time.
Akira proudly revealed his new creation to Erika.
"Behold! My new creation, Yoriichi Type Null!" he declared with a grin.
Erika stared at it.
Stared some more.
Then slowly turned her head toward Akira.
"…You were supposed to make a Yoriichi Type Zero robot," she said flatly. "So why… does this look like a six-armed General Grievous?"
Akira blinked.
Then looked at the machine.
Then back at her.
Akira crossed his arms proudly.
"Well… it looks cooler this way, right?"
Erika sighed and rubbed her forehead.
"…Just hope it works well," she sighed. "We have the demonstration today."