Hearing the two talk about him, Tanjiro looked away, a hint of worry creeping into his eyes.
Muichiro noticed the change and spoke softly.
"Is Tanjiro worried the medicine won't work?"
"…No, Miss Tamayo's pharmaceutical skills are exceptionally high, there's nothing to worry about."
Tanjiro averted his gaze.
"I'm just a little worried about myself after I turn back into a human."
"Tanjiro will have the power of a Hashira too, right? Then we'll be able to fight together, isn't that great?"
"But those are all bonuses that come with being a demon."
Tanjiro lowered his eyes to his hands.
"I don't know if I'll still be able to master the Breathing Styles like I do now after I turn back into a human. Plus, I heard Tamayo mention before that some demons who revert to human form lose their memories from when they were demons. But I don't want to forget everyone… I'm… really confused."
Muichiro froze slightly, unsure how to respond. Hiru, however, noticed the exchange and raised his voice a little.
"More than that, you're probably worried about the possibility of shrinking, aren't you?"
Seeing Tanjiro's bewildered expression, Hiru sighed.
"Ninety percent of demons who revert to human form return to their human-era appearance. In other words, once you take the potion…"
After a few seconds of blankness, Tanjiro's expression turned panicked.
"So… does that mean after I take the human-restoration potion, I'll likely revert to the age I was when I became a demon?"
"Barring any surprises."
"Eh…"
Muichiro looked at the stiffened Tanjiro.
"So… that means I'll be Tanjiro's older brother then?"
Tanjiro: !!!
Ignoring Tanjiro, who had fallen into a mental spiral, Hiru continued discussing pharmacology and Slayer Marks with Tamayo. It wasn't until Muichiro began to grow sleepy that Hiru finally took his leave.
Later, Uzui came to the Rengoku estate to find Hiru. He explained that he had looked into Zenitsu. Although the boy was well-suited for Sound Breathing, he stubbornly refused to take him as a teacher and insisted on learning Thunder Breathing instead. In the end, Uzui had only given him some pointers before leaving it at that.
Hiru simply thanked Uzui and did not press further.
A week later, Tamayo produced the prepared medicine as promised. However, when Tanjiro received it, he felt an overwhelming sense of pressure.
Aside from Nezuko and Takeo, who had specifically taken leave from squad training to be present, and Tanjiro himself along with Tamayo, everyone else present was a Hashira-level swordsman.
Under the gaze of so many people, Tanjiro inevitably grew nervous.
"Um… this many people?"
"After all, this is the first time they've heard that a demon can turn back into a human. It's only natural they're curious."
Hiru scanned the surroundings, his brows tightly knit.
"Seriously… isn't he here yet?"
Tanjiro looked up at Hiru.
"Hiru-san, are you talking about teacher?"
"Yes. Can you smell him?"
Tanjiro sniffed lightly, then froze. Just as he was about to say something, his body suddenly trembled, and his expression twisted with conflict.
Seeing that uneasy look, Hiru immediately understood that Tanjiro had realized something. His brows furrowed, but he said nothing. He simply had Tanjiro lie down and prepare for the injection.
Once Tanjiro was ready, Tamayo stepped forward with a syringe filled with the medicine. She inserted the needle into his arm, and as the plunger was pressed, the faintly bluish liquid was fully injected into his body.
After the injection, Tanjiro quickly fell into a deep sleep. As time passed, his body began to react.
Slayer Marks spread from his forehead. The fangs and claws that had been retracted extended once more, accompanied by a painful growl rising from his throat.
Hiru frowned at the sight. This was not his first time witnessing a demon being turned back into a human, but Tanjiro's reaction was the most severe he had ever seen.
Tamayo, standing nearby, remained calm. She took out a second vial and injected it into Tanjiro.
As the medicine took effect, the signs of his demonization receded slightly. However, the Slayer Marks covering his face did not fade. Instead, they grew even more vivid as his breathing became increasingly rapid.
As the marks deepened in color, Tanjiro raised a hand to clutch his head, and a pained roar tore from his throat once again.
"This won't work. This kid's talent as a demon is far too strong…"
Hiru pressed him down just before he could start struggling.
"Do you have more medicine? Give him everything."
Tamayo finally frowned. She picked up the remaining three vials and injected them all into Tanjiro as instructed.
"I only had enough materials for these doses. If this fails, it will be difficult to proceed."
"We can only rely on his willpower now…"
Hiru stared at Tanjiro, whose clothes were already soaked through with cold sweat, his brows tightly drawn.
"We've already done everything we can."
Nezuko stepped forward unconsciously, her hands clasped tightly in front of her forehead.
"Please, onii-chan… come back…"
Takeo, his face filled with worry, silently stepped forward and wrapped an arm around Nezuko's shoulders. Watching Tanjiro with his eyes tightly shut, he too prayed silently.
...
After the injection, Tanjiro felt his entire body grow light, as if he were floating. It was like being immersed in warm water, so comfortable that it made him drowsy.
But just as his consciousness was about to slip away completely, a cold voice echoed from deep within his mind, snapping him back to awareness.
The voice seemed to rise from the depths of an abyss. Even though it was indistinct, the malice within it was unmistakable, making one instinctively want to flee.
"Another one dead… useless…"
[Who's speaking? This voice… I feel like I've heard it somewhere before…]
"Demon Slayer Corps… damn it… you vermin…"
[Demon Slayer Corps? Is it an enemy? No… I need to focus more… I have to concentrate harder to hear clearly…]
As his focus sharpened, Tanjiro's vision suddenly cleared.
What appeared before him was a maze of overlapping rooms. Some were intact, while others were covered in deep sword slashes. Those marks felt strangely familiar.
Before he could make sense of it, his perspective shifted, and he looked toward a figure with pale, oak-colored hair.
"Doma, did you retrieve the paintings from Daki's place?"
The man looked up, his tone light and cheerful.
"I got there just in time, so I recovered everything~ Though it's a pity about little Daki and her dear Gyutaro~"
Tanjiro clearly saw the words "Upper Moon One" etched within the man's multicolored eyes. Startled, he instinctively tried to look back again for a closer look as his gaze moved away.
But the moment that thought arose, the cold and furious voice rang out once more.
"You ignorant fool. Get out."
In an instant, Tanjiro's vision was swallowed by darkness again.