The moment Tanjiro heard that Hiru had come specifically to see them, he immediately straightened up.
"I practice controlling my appetite every night. On our last mission, when I ran into a child with Rare Blood, I didn't react at all."
"It's not that I think you came to check on me… Since you allowed me to operate independently after passing your brother's test, I'm confident in my self-control."
"Is this about Takeo's Breathing?" Tanjiro tilted his head, a faint crease of concern on his brow. "Since he's learned more than one style, he sometimes slips back into Wind Breathing—the first one he learned—without realizing it during combat.
"Lately I've been helping him maintain the constant state of Total Concentration, hoping it'll make it easier for him to fully grasp the Moon Breathing your older brother taught him. But whenever his focus wavers, it falls apart and he reverts to Wind. It leaves him drained almost every time…"
Hiru: …The constant state? Isn't that something usually expected of Hashira? Takeo just joined the Corps—aren't they pushing him too hard?
As if catching on to Hiru's confusion, Tanjiro hurried to explain.
"Teacher said keeping it up all the time builds stamina steadily, so the earlier you start, the better. And after your older brother taught Takeo Moon Breathing, he asked me to help him train like this before disappearing somewhere. Since I don't need much rest, it's easier for me to practice alongside Takeo and Nezuko…"
"…You're so good at saying what I'm about to say that you're making me look like an idiot. Stop. Don't talk. Just listen."
Tanjiro blinked.
"?"
Hiru let out a long sigh and pinched the bridge of his nose. After a moment, under the obedient stares of the three children, he muttered quietly,
"What was I about to say again?"
...
Inosuke felt oddly light, like his body wasn't fully there. He remembered sensing something strong—something that made his blood roar. He'd grabbed his blades and rushed out without thinking…
And then?
Why was he back here?
He stared at the blanket covering him, frowning in confusion.
But the confusion didn't last long. His fighting spirit sparked again as his eyes landed on the man sitting with his back turned, deep in thought. That familiar thrill crept up his spine.
That's it. That's where the danger came from.
No doubt.
This guy was stronger than that box-demon who made him feel all floaty. This was a real fight.
Moving with exaggerated stealth, Inosuke slowly peeled back the blanket and flattened himself against the tatami, inching closer.
[Leaving your back wide open like that? You wouldn't last a day in the mountains! I'll show you what happens when you let your guard down! Take this—hm?]
"Is there even one normal person in this Demon Slayer Corps besides Nezuko?"
Without turning, Hiru casually reached back and pressed a hand down, pinning Inosuke to the floor. His voice carried exhausted disbelief. When he noticed Takeo's stunned expression, he sounded even more drained.
"You all kill demons without blinking. What part of that sounds normal? There aren't many normal people in this Corps to begin with."
Tanjiro looked like he wanted to argue, but thought better of it and quietly straightened his posture.
Hiru lifted his hand, knocked Inosuke out cleanly, and tossed him back under the blanket.
"Forget it. If I can't remember it now, it probably wasn't important. Get some rest."
"Wait, Mr. Hiru." Tanjiro raised his hand again. "I've developed a Blood Demon Art and would like to test it. Could you spar with me? With Teacher's help, I've completed part of it, but there are still some effects I can't fully confirm."
Hiru nodded once and gestured for him to follow.
Left behind, Takeo and Nezuko exchanged a glance.
Nezuko wished them goodnight and returned to the next room. Takeo carefully tucked Inosuke in, then sat cross-legged and resumed his constant breathing training.
To this day, Takeo didn't know his instructor's name. He only knew the man was the elder brother of Mr. Yoriichi and Mr. Hiru—a demon with extraordinary swordsmanship and a frightening reluctance to speak.
At first, even with Tanjiro nearby, Takeo had been terrified of him. Every swing of that wooden sword felt less like instruction and more like an execution attempt.
Strict. Unbending. Cold.
That was Takeo's impression. Over time, the fear didn't disappear—it simply settled into him, becoming something heavier.
Whenever he made a mistake, even if the teacher merely looked at him in silence, Takeo felt an almost crushing urge to kneel and beg forgiveness.
Thankfully, once the teacher confirmed that he had mastered the breathing pattern of Moon Breathing and memorized the first six forms created during his human years, he left just as quietly as he had arrived.
No farewell. No explanation.
Takeo had felt relief.
And something like disappointment.
There had been a bond, however brief. Arriving without a word and leaving without one felt… distant.
Still, he was grateful.
Moon Breathing suited him far better than Wind Breathing ever had. With it, his breath flowed smoothly, without resistance. There was even a faint, barely perceptible sense of rightness—like he had only just begun to breathe properly.
And strength meant he would no longer have to stand by helplessly while tragedy unfolded.
The teacher had explained that only the first six of Moon Breathing's sixteen forms were created while he was human and could safely be used by a human body. The remaining ten were developed after he became a demon. They could inspire evolution—but not be copied directly.
Yet something felt off.
After becoming a demon, he hadn't discarded those six forms.
He had perfected them.
Refined them to limits meant for a demon's body.
Takeo would never forget the first time he used Moon Breathing to kill a demon.
One strike.
That was all it took.
And that was all he could manage.
The backlash cracked the bones in his wrist. Muscles tore. His lungs burned with the metallic taste of blood. He hadn't even been able to unleash the form at full power.
And still—
That incomplete strike tore the demon apart effortlessly. Beneath the sweeping arcs of moonlight, there hadn't even been ashes left to see.
In the most recent battle, he had used Moon Breathing again. Even while holding back, he had nearly crippled himself in the process.
It was humiliating.
What consumed his thoughts now was how to soften those forms—how to reshape them into something sustainable.
Otherwise, collapsing after a single strike would make him dead weight.
[Brother once said Sun Breathing is ultimately a single continuous technique—the first twelve forms combined into one strike.
Then… could Moon Breathing be broken down as well?
If so, what would define that division? What would each part look like once separated? And how was Sun Breathing divided in the first place?]
Kamado Takeo decided it was worth trying.