Inside a dimly lit room where even the faintest sunlight could not reach, papers and handwritten notes were scattered across a low wooden table. Medical diagrams, poison formulas, sketches of cells, and half-finished drafts of antidotes lay open under the soft glow of lantern light.
Akira sat with Tamayo, Shinobu, and Yushiro around the table. The air smelled faintly of herbs and ink, evidence of long hours spent researching.
Tamayo gently placed a parchment down and folded her hands.
"Nezuko's body is already vastly different from other demons," she explained. "She has developed antibodies against Muzan's cells. And these blue cells we discovered, are you certain they came from the Blue Spider Lily you mentioned?"
Akira nodded without hesitation.
"Yes. Tanjiro said their mother used to make tea with those flowers whenever they caught a cold."
Tamayo froze, stunned.
"To think… the flower Muzan has searched for over a thousand years was used as tea for colds." A small, elegant sigh escaped her lips. "If he ever learns that, I wonder how he will react."
Akira leaned back with a mischievous grin. "Don't worry. When I meet him, I'll make sure to tell him. I'll roast him with that information first, then roast him in the sunlight."
That comment even made Shinobu giggle softly, covering her mouth with a hand.
Akira then turned toward Tamayo again, glancing briefly at Nezuko, who sat a little distance away, happily playing with Erika like an innocent child.
"Tamayo-san, earlier you said you already have an idea for a medicine to turn her back into a human, right?"
Tamayo nodded slowly.
"I do have plans. But we must ensure the formula is perfect before we attempt it on Nezuko."
Akira waved a hand reassuringly. "Don't worry. Give me every medicine you've created so far, and the ones you plan to create. We can test them on Nezuko's blood. With my powers, we can accelerate the reactions and see the results instantly."
And so the discussion began, covering treatment methods, dosage theories, and the delicate steps needed to reverse demonic biology.
They continued their discussion for some time, papers and ink brushes scattered across the low table as Tamayo and Shinobu carefully organized each set of notes. Eventually, their conversation shifted to an even more pressing concern.
"We also need to stop Muzan from dividing the way he did in the past," Tamayo said quietly. "Otherwise, he will simply escape again."
Akira nodded, as if he had been waiting for that topic. "Yes. Actually, I prepared something for that too."
He reached into his storage and produced a small pink flower.
Tamayo tilted her head. "What is this?"
"A flower called Madagascar periwinkle," Akira explained. "It's from another country."
Shinobu blinked in surprise. "Is that the flower you asked Oyakata-sama to obtain for you?"
"Yep," Akira replied. "They don't grow anywhere in Japan, so I needed help to import them."
Tamayo examined the flower closely, her expression sharpening. "And what exactly does it do?"
Akira leaned forward slightly, tapping the flower with a finger. "Vincristine and Vinblastine. They're powerful chemotherapy drugs. Simply put, they stop mitotic cell division. If I tinker with them using my power, I'm sure we can stop Muzan from dividing and escaping."
Shinobu frowned thoughtfully. "I've never used these before. Are they truly that strong?"
Akira nodded with absolute confidence. "Don't worry. If my calculations are correct, I'm sure this will work."
Both Tamayo and Shinobu exchanged a glance. They already knew, when Akira said his calculations were correct, he had never once been wrong. Not in a situation that mattered.
So the four of them spent the rest of the evening refining antidotes, poisons, and potential formulas, discussing every theory, every method, and every possible outcome. Time moved quickly, unnoticed.
By the time they finally looked up from the table, the lantern flames had burned low.
It was already very late, and the night had long fallen.
Akira stretched his arms as he rose from his seat.
"Well, it's already late," he said. "Let's continue the experiments tomorrow."
But before he could take a single step, both Shinobu and Tamayo immediately objected.
"Can we not continue tonight?" Tamayo asked. "As a demon, I do not tire easily."
"And I'm a Demon Slayer," Shinobu added. "I'm used to sleepless nights."
Akira shook his head firmly. "Nope. I still need to prepare for the Hashira training, and I'm busy with other things too. But…" He tapped the stack of papers beside him. "You can try creating these medicines from the formulas I gave you. Test how they behave. What do you think?"
The two women exchanged thoughtful looks. After a moment, both nodded.
"That will do," Tamayo agreed softly.
"Very well," Shinobu said. "We'll begin immediately."
With that settled, Nezuko remained behind with them, safe under the protection of the three former Hashira who waited in the other room.
Akira already knew who they were.
The former Water Hashira and the former Thunder Hashira looked exactly as he imagined, calm, sharp, and intimidating in that dignified veteran way.
But the former Flame Hashira… Rengoku's father…
Akira blinked twice. He looked completely different from how he appeared in the anime.
"Wasn't he supposed to be a drunk mess?"
Instead, the man radiated quiet strength and awareness, like someone who had clawed his way back from despair.
"Maybe hearing his son fight an Upper Rank changed him", Akira thought.
"Or maybe, with the final battle approaching, he decided to stand straight again. Well… the world keeps moving no matter what".
Still, there was something Akira needed to ask, specifically from one of them.
He turned toward the elderly Thunder Hashira, his expression serious.
"Excuse me," Akira said. "Old man Thunder Hashira… there's something I want to ask you. Or rather, something I want to request."
The elder, far older than the other two retired Hashira, opened one eye lazily as if waking from a long meditation.
"Speak."
Akira met his gaze seriously. "Can you teach me the rest of the Thunder Breathing forms?"
Erika blinked beside him, confused. Why does he suddenly need Thunder Breathing…?
The Thunder Elder continued to study Akira in silence. "What do you mean, 'the rest of them'?"
"Well," Akira replied, "I learned all the breathing styles already, but for Thunder Breathing, I only know the first form. So I want to learn the remaining forms from you, so I can complete it fully."
The old man grunted thoughtfully.
"Before I decide… show me your style. This 'Star Breathing' you created."
At that, the other two former Hashira, Urokodaki and Shinjuro, also looked up with clear interest. They had heard the rumors: the mysterious boy who created his own breathing style, the boy who had defeated Upper Ranks. Seeing it with their own eyes was another matter entirely, so they are also curious.
Akira nodded. "Sure. I'll show you. Answer me—Eclipse."
In an instant, the jet-black armor wrapped around him, its presence overwhelming. Even though they'd heard of the armor, this was the first time any of the retired Hashira had seen it. Their eyes widened, some in awe, some in disbelief.
Twin katanas materialized in Akira's hands.
He set his sights on a tree nearby.
"Star Breathing—First Form… Flashing Comet."
He vanished.
A single blink later, he reappeared behind the tree as it split cleanly in two.
An instant later, he reappeared behind the tree, blades lowered in calm silence.
The thick trunk split cleanly in half.
Akira dispelled his armor and turned back toward the old man. "How is it?"
Shock washed across all three Hashira.
But none more so than the elder of Thunder. That speed…faster than Thunder Breathing, faster than any student he had ever trained.
Akira stood proudly… until the cut tree toppled.
CRASH!
The impact knocked into the next tree.
CRAAACK!
That tree fell into another.
Then another.
And another.
Under the horrified stares of everyone present, the forest collapsed in a long, unstoppable chain reaction, a full domino effect.
Within seconds, the once-hidden house was no longer hidden at all. Nearly the entire clearing was exposed.
Akira stared blankly at the destruction.
"What the hell kind of cartoon thing is this? Did the universe forget I'm inside an anime?!"
From the house, Shinobu stepped out slowly. Her eyes scanned the field of fallen trees… and then landed on Akira.
Her smile was gentle.
Her eyes… absolutely were not.
"Akira-san," she asked sweetly, "what is this?"
Akira instinctively glanced at Erika for backup.
But Erika immediately looked away, pretending she had never met him in her life.
Cornered, Akira straightened his back and answered with completely manufactured confidence:
"Well… I was collecting firewood. We have to prepare ourselves. The winter is coming."
He said it with such seriousness that one would think the White Walkers were approaching Japan.
In the end, Akira's excuse did not convince anyone.
He still had to repair every fallen tree using his powers. It took some time, more time than he wanted to admit, but since he had caused the mess, there was no escaping the responsibility. When the last trunk finally slid back into place and the forest looked whole again, the former Thunder Hashira studied Akira with a long, appraising look.
A faint smile tugged at the old man's lips.
"Very well, kid. I will teach you."
Akira bowed deeply, relief washing over his face. "Thank you."
At least his sacrifices, the humiliation, the scolding, and the impromptu forest reconstruction weren't in vain.
The lesson began immediately. And ended almost just as fast.
The old Thunder Hashira demonstrated the breathing forms one by one, slow enough that a normal prodigy might need weeks or months to grasp the fundamentals. Akira, however, merely watched each movement once and then reproduced them with flawless accuracy on the spot.
The former Hashira trio stood frozen, eyes wide.
He had shocked all of them again.
But at least the goal was achieved; Akira now possessed every form of Thunder Breathing.
When the training concluded, Akira bowed once more. "Thank you for teaching me."
Erika offered the old man a polite bow as well before following Akira out of the clearing. When they were far enough away, she finally voiced the question that had been lingering since he first made the request.
"Do you really need to learn Thunder Breathing?"
Akira nodded without hesitation. "Well, my Star Breathing is all about speed, at least the first form is. Learning Thunder Breathing helps with that. And now I know all the breathing techniques, so it's a good thing, right? I finally completed my collection. I learned all breathing styles."
A beat of silence followed.
Then Selena's telepathic voice cut in, sweet as ever, "Brother… what about Moon Breathing?"
Akira stopped walking.
His eyes widened slightly.
"…oh."
He had actually forgotten.
He rubbed the back of his neck, embarrassed. "Well… who knows. Maybe later I'll learn it from him during the fight, like I always do, learning in the middle of a battle is my specialty," Akira said with a confident smile.
Erika didn't bother replying. She simply gave him a long, silent stare, the kind that clearly said I am judging you, before turning away and walking ahead. Akira followed after her, unfazed.
They returned to the Butterfly Mansion and rested for the night. Erika still drank her daily blood, though she didn't bite his ears this time.
By the next morning, both of them woke early, preparing for the start of Hashira Training. The air was crisp, and the mansion grounds were unusually quiet as Akira and Erika walked side by side toward the shed behind the Butterfly Mansion.
Erika glanced at him.
"So… what exactly are we going to do for Hashira Training?"
Akira folded his arms thoughtfully.
"I actually planned something a while ago. I made it just for fun, but considering the situation, it might work even better than I expected."
Erika raised a brow, suspicious.
"And what is it?"
"You'll see," Akira said, a mysterious glint in his eyes.
He slid open the shed door with a creak. Seeing that they were finally alone, he reached into his inventory.
When he pulled the object out.
Erika froze.
Her expression twisted into pure shock, almost horror.
"What… the hell is that?"