Tanjiro jolted upright, his right hand clutching the sweat-soaked fabric over his chest as he gasped for air. The sensation of falling into an abyss still lingered, yet what burned inside him now was pure rage.
The only one Upper Moon One would treat with such respect was the one who had attacked his family: Muzan Kibutsuji.
[ What was that? Why could I see what Muzan was seeing? What is he doing? Was that the Infinity Castle? ]
"…Onii-san?"
Tanjiro turned his head slightly. Nezuko and Takeo's worried faces reflected in his eyes. He opened his mouth, trying to comfort them, but his throat felt stuffed with cotton, and not a single word would come out.
A wrenching pain twisted through his internal organs. He gripped his chest tighter, doubling over as he struggled to breathe. Something inside him was changing violently, and the pain was unbearable.
[Breathing… will Breathing Styles help? Ugh. No, it hurts. It hurts so much I want to scream. It feels like my whole body is being twisted and rebuilt.
No… no. I have to endure it, Tanjiro. Nezuko and Takeo will worry. And the pain is a good sign. It means the medicine is working. As long as… as long as…]
Cold sweat slid down his jaw, gathering before dripping heavily onto the ground.
His condition was strange. The signs of demonization on his body had faded, yet only one of his pupils had returned to a human round shape. That should have been a good sign, but as time passed, the round pupil began to sharpen again at both ends.
The sight threw Nezuko and Takeo into panic.
Nezuko rushed forward and grabbed his arm, her voice trembling with tears.
"Onii-chan! Don't lose! You have to turn back into a human! Please… I'm begging you!"
"Ne…zuko…" Veins bulged along his arm as he clutched his clothes. His voice was hoarse and dry. Even in such pain, he forced a smile. "I'm… I'm fine… Onii-chan won't… won't lose…"
"Onii-san, Breathing Styles. Keep breathing!" Takeo said anxiously. "Didn't Mr. Yoriichi say it? The Sun Breathing Technique suppresses a demon's regeneration. Miss Tamayo doesn't have any more medicine. You can't lose. Hurry and breathe!"
Tanjiro lowered his head and forced himself to use his Breathing Styles despite the pain. The searing sensation from when he first became a demon surged back violently. Visible streams of air formed at his lips, but his breathing wouldn't stabilize, and it failed to stop the spread of the demonic marks.
"Hey, hey… I've never heard of something like this," Hiru said with a grave expression. "Tamayo, are you really out of medicine?"
"I turned all the materials I obtained into medicine because you said Tanjiro had exceptional talent as a demon…" Tamayo shook her head slightly. "It seems we may fail this time."
Hiru clicked his tongue and grabbed Tanjiro just as he tried to hurt himself to relieve the pain.
"Stop dragging this out, brat! It's already come to this. Just turn back into a human already! Do you really like being a demon that much?"
"S-sorry…"
Even restrained, Tanjiro continued trying to maintain his Breathing Styles. The change in his pupils slowed slightly, but it did not stop.
Hiru could feel how tense his body was. The pain had to be unbearable, yet all he could do was hold him down to keep him from injuring himself. From the moment the medicine was injected, this was a battle only he could fight. Outside help would hardly change the outcome.
The surrounding Hashira frowned, exchanging glances as they whispered among themselves.
"Sigh…"
The soft sigh, as if spoken right beside their ears, startled everyone. When they looked again, the masked, white-haired youth had already appeared silently beside Tanjiro.
He raised a finger and pressed it against his forehead.
"Tanjiro, focus."
"Te… Teacher… I'm sorry, I… I can't…"
"Focus."
Looking up at that unchanged expression, the unease in his heart finally settled.
"…Yes, Teacher."
"As I said before, the Transparent World is not an extension of sight. It is the outward projection of senses honed to their absolute limit. But now, you must turn that perception inward and direct it into your own body.
You will clearly sense that the Blood Demon Art is suppressing the medicine. What you must do is use your Breathing Styles to drive it out. Destroy it completely so the medicine can take effect.
If the pain in your lungs makes sustained breathing impossible, switch to short, rapid breaths. The clash will be painful. But Tanjiro… your family is waiting for you. You must succeed."
"Yes…"
His voice trembled with pain. Eyes shut tight, he followed the instructions, shifting to short, rapid breaths. Though still unstable, the Slayer Marks that had been spreading began to fade.
Gradually, his breathing lengthened and steadied. The marks retreated back to his forehead. Sweat still poured down, and the pain had yet to pass.
The sun rose and set.
Then rose again.
Light spilled into the room as a gentle morning breeze slipped through the window, brushing past everyone as if curious about what had happened.
His body, drenched in cold sweat, finally began to feel warmth and chill again. The hazy memories in his mind slowly cleared.
The breeze made him shiver.
Looking at the sunlight streaming in, he smiled through tears.
"I'm sorry… I've caused everyone so much trouble these past few years."