Hiru watched Ibuki—his ears flushed red—struggle helplessly against Iwayuki's grip until his limbs finally went limp and he was released. Silently, Hiru compared his own height to his brother's, then exhaled in relief.
Thankfully, though his brother was tall, he wasn't some muscle-bound brute. Even if he held Hiru like that, he wouldn't suffocate—ugh, not that his brother would ever do such a thing anyway, but… could he even hold his breath?
Still, he couldn't help feeling a little envious. Neither of his brothers was good at showing affection, so physical contact between them was rare—at most, a pat on the head or a hand on the shoulder. If only...
Catching his younger brother's curious gaze, Yoriichi could only return a puzzled look.
"Ahem, let me continue."
Hiru snapped back to his thoughts and cleared his throat awkwardly, deliberately avoiding Ibuki, who was still trying to breathe in fresh air beside him.
"The main step of the second experiment is to prepare another batch of the demon-transforming drug, then use it to turn someone into a demon."
At those words, everyone present except Yoriichi frowned. Ibuki opened his mouth to speak but, noticing Iwayuki's hand still resting on his shoulder, thought better of it and stayed quiet.
"But don't worry. If it works, I'll choose mountain bandits and robbers—people who serve no purpose to society—for the experiment. No ordinary people will be harmed.
Then I'll let this newly created primordial demon feed enough to gain strength."
Hiru swept his gaze over the grim expressions of the Hashira before continuing.
"Next, I'll have it infect other bandits with its blood, then kill it to see if those transformed bandits die. If they don't, I'll test whether their blood remains infectious.
If the first batch of infected bandits die from the Primordial Oni's corruption, or if the transformed oni lose their infectious ability, then when my brother reaches the end of his life, I'll turn him into an oni infected by me. We'll then go into hiding until Muzan Kibutsuji reappears. My brother and I will take on the duty of slaying him, and after ensuring no demons remain in this world, we'll face death together.
On the other hand, if the infected demons still retain infectious blood, then when my brother's body begins to fail, I'll choose death myself. Of course, if I've developed the human-restoration drug by then, I'll take it and return to being human... but judging by my current progress, well—chances are, I'll just end up sunbathing."
"Hmm, using mountain bandits, huh? That's practically a public service," Keijin said, folding his arms. "By the way, death row inmates wouldn't be a bad choice either, you know?"
"Mr. Keijin!" Oborozuki shot him a sharp look. "No matter how you justify it, using humans for experiments is far too—"
"Those scum dying wouldn't matter," Keijin muttered, scratching the back of his neck where the hairs stood on end. "But if Mr. Yoriichi really turned into a demon, could anyone actually destroy him?"
"That's exactly why the experiment's necessary," Hiru sighed. "If the primordial demon dies but those it infected survive and can still spread the curse, then I'd never dare let my brother become a demon. In that case, who could possibly stop him…"
"Indeed. If Mr. Yoriichi were to become a demon… it would be a disaster for humanity."
Yoriichi lowered his head, quietly rubbing the hilt of his sword, silent and thoughtful.
"There's no need to tie ourselves in knots over a mere possibility!"
All eyes turned toward Rengoku Tetsushiro, who stood with his arms crossed, a radiant smile on his face.
"A swordsman's heart is strong and unyielding! Mr. Yoriichi is the finest example of that!
Besides, if Mr. Hiru can do it, there's no reason Mr. Yoriichi couldn't as well!"
His bright gaze shifted to Yoriichi.
"No matter what decision you make in the end, Master Yoriichi, you'll always remain that kind and mighty swordsman! You shine as brilliantly as your sword forms. Even as a demon, you would surely remain upright and righteous!"
Hanyu Ichiyo looked displeased, but before he could speak, Rengoku Tetsushiro continued, voice clear and bold.
"And forgive my bluntness! With Mr. Hiru's talent—the kind capable of turning a demon-slaying medicine into one that restores humanity—this so-called experiment might just remain a distant hypothesis forever!"
"...Pfft."
No one knew who let out the sound, but the tension in the room finally broke. Even Hanyu Ichiyo, who had never liked Hiru, couldn't help but twitch his lips.
Yoriichi chuckled softly, reaching out to pat Hiru's head.
"Indeed."
Hiru: …
Hiru glared at Rengoku Tetsushiro.
Thanks a lot, you owl!
Plop.
The rain that had been gathering in the clouds finally began to fall, adding a chill to the early autumn air.
"Today's Hashira meeting is adjourned," Ubuyashiki Asahi said, rising to his feet. "Please, everyone, come inside and rest out of the rain."
"Then I shall not refuse such kindness."
"Oh, then I'll take you up on that."
"We are most grateful for your hospitality, Master!"
"Thank you, Master."
The swordsmen spoke one after another, stepping into the mansion.
Yoriichi lifted his box and walked to the veranda, nodding slightly toward Ubuyashiki Asahi.
"Thank you for your kindness."
"No, I should be the one saying that," Ubuyashiki replied, looking up at the tall swordsman. "Without your selfless teaching of the Breathing Styles, the Demon Slayer Corps would be in far worse shape. Once again, thank you for your generosity."
Yoriichi crouched down to meet his gaze, a gentle smile on his lips.
"No, it's I who should thank you—for recognizing Hiru's existence. Truly, I'm deeply grateful."
"Mr. Hiru hasn't eaten humans or taken lives since becoming a demon, has he?" Ubuyashiki smiled. "Though his attitude toward humans isn't exactly kind—and he's even attacked Demon Slayers on occasion—each time was to protect you, and always because someone had spoken ill of you first.
Not to mention, Mr. Hiru has unintentionally developed medicines that have been invaluable to the Corps.
So I believe he's still someone who can be reasoned with—a being who still retains his humanity."
"That's not right."
Standing out in the rain, Hiru turned upon hearing this. He walked slowly under the eaves and knelt before Ubuyashiki.
"That way of thinking is wrong. Once a person becomes a demon, nothing remains but their obsession. So please, remember this well—demons are not beings capable of communication."
Having said that, Hiru stepped back into the rain and left without another word.
Ubuyashiki noticed the sorrow clouding Yoriichi's face after Hiru's words, though it quickly softened back into calm. Yoriichi nodded politely, murmured his farewell, then picked up his box and followed after Hiru.
Ubuyashiki stood motionless, watching their retreating figures disappear into the rain, an indescribable feeling tightening in his chest. That evening, when he went to speak with them again, he was told they had departed once the rain had stopped.
He could only keep his unspoken words in his heart, resolving to share them the next time they met.
But after that day, Ubuyashiki Asahi never saw the two of them again.