Morning was harsh; today the old man, Kiryuu Gen'un—whose name Arai already knew—was to teach him the basics of Mist Breathing.
It was true he had taught him before, but back then it was mostly breathing itself, not the Mist yet.
The snow in the yard had crusted; the view was clean and direct. Arai stood in the morning cold, bandage wrapped tight around his chest, his father's knife at his side. Kiryuu stood a short distance away, watching him.
"Start breathing. Not fast. Not slow. Just as your body tells you—no panic," he ordered.
Arai nodded. He held his breath for a few seconds and then released it. He had no intention of imitating the others; his body responded in its own way—broken exhale, cough, brief pause. Kiryuu did not exchange a look with Kenzō, who had just left—one of his few successful students, and the one who knew what he was seeing.
Kenzō had stayed for three days, having taken serious injuries in battle; the Demon Slayer Corps had ordered him a few days of rest, which he planned to—and did—spend with his master. He even brought him a new apprentice.
"The style I'm teaching you—the Mist—requires rhythm," the old man said later, standing by a curtain of cloth hung for cutting.
"Mist flows. Your mist breaks. That isn't a mistake. It's a fact. We have to use it."
The first hours were repetition of fundamentals. The other students—three younger men and a young woman—trained at the same time. They ran the field, climbed a rope, kept balance on a beam. Their breathing was even, smooth. Kobayashi Ryō, the strongest among them, led the group. He had a sharp expression and a voice that didn't need raising.
He had trouble with Arai on the very first day. Kiryuu put him on the run with the others.
"Come on, Arai, don't play around," Ryō said when Arai slowed during the run. "If you can't keep pace, you're wasting time here."
Arai felt no anger. Only cold focus. "I'm working," he answered quietly.
Ryō looked at him with contempt. "Working? How? By walking instead of running?"
"My body isn't used to long walking yet, let alone running," he said after a bout of coughing.
Ryō wasted no time and quickly overtook him. "I heard you've got some serious illness or something. I don't get how someone like that even tries to be a Demon Slayer."
---
Training went in series. Kiryuu divided the day into blocks: sword fundamentals, balance drills, breathing sessions in cold water, sword work against falling targets, and a separate practice for Mist Breathing—which the old man called "shaping the breath." Everything was precise, repeated, free of needless words.
In one of the breathing sessions, Arai stood waist-deep in a mountain spring. The cold stung his lips; his breathing changed. He felt every inhale magnified, every exhale leaving bubbles in the water that vanished.
He tried to find evenness—but evenness meant pain in his chest, especially when he tried to keep pace with the others. After three repetitions he fell to his knees and the coughing knocked him down. Water splashed around him.
The old man didn't scold him. He only bent down and laid a palm on his back, feeling the lungs work. "Hold," he said. "Don't lose the rhythm. When a fit comes, it's not the breathing that kills you. It's giving up between breaths."
Arai rose slowly. Ryō watched. Their rivalry was born from differences. Ryō trained by numbers, by time, by measure.
Arai relied on a way the others didn't understand: interrupted breath, short bursts, unpredictability. Kobayashi Ryō couldn't see himself in it at all; he took it as weakness, not tactic.
"Your coughing is disruptive," Ryō said one evening during target practice. "If you can't get rid of it, at least learn to hide it."
Arai turned. His eyes were cold. "I don't want to hide what's mine," he replied. "I'll learn to use it."
Kiryuu watched the exchange in silence. Then Arai lifted his sword again and traced a series of quick cuts.
His movements were broken, uneven—yet in that brokenness there was intent. A sharp jerk, a pause, a lunge. With one strike he sliced a smaller target with a precision that left Ryō without words.
"There's something different in him," Kiryuu told Ryō later, when he called them both to the fire. "He may be ill, but he has every mark of a strong Demon Slayer: he doesn't give up, he stays cool when it matters, he keeps finding ways to track anything by any means—and, most importantly, he has potential."
Ryō didn't admit the unease he felt. The rivalry changed his expression. He watched Arai more closely each day. He tried to imitate those jerking cuts, but his body sought balance Arai refused to grant it. While Arai lost his breath and found it again, Ryō sank into a puzzle.
Arai wasn't talkative at all; he focused only on training. That was the opposite of Ryō, who could be called the students' leader. And Arai spoke with no one but Kiryuu.
It wasn't that he feared speaking; it just wasn't a priority. He lagged far behind under Kiryuu, and for now he was by far the weakest. Getting stronger was one of his biggest goals.
Training didn't start and end with physical drills. In the following days, he learned the forms of Mist Breathing with Kiryuu. He explained how mists could cover a step, how deception could be stronger than strength.
He showed small details: how to stand, how to correct one's steps, where to place the body's weight in a cut so the guard became irregular. Arai tried to copy.
His movements were chaotic, not graceful, but there was truth in them—when he coughed mid-movement, the instant opening he created brought the target into an unusual contact with the blade.
"Your body is trying to talk to you," Kiryuu said on one late night when Arai stayed after training. "And you'll teach it to talk in a way that hurts. I won't teach you only by the book. I'll force you to try."
And so they tried. They let a velvet cloth drop behind him to practice attacks on it. They set him against an irregular opponent—a dummy on a spring that snapped back after every cut.
They practiced fighting in the dark, with only moonlight filtering through the trees. They practiced transitions from jump to fall, when Arai had little breath and even less strength. In each of these drills Arai found that his weakness made room for unique solutions. Not speed. Not power. Precision in interruption.
Life at Kiryuu's homestead was part of the training, too. Arai slept in a small room with wooden floors next to the other students; their huts stood tight side by side. Morning duties included drawing water, preparing food, and sharpening blades.
Those small tasks became a way to build a body that could adapt. Every chore repeated. Every morning followed the same cycle. That repetition, they said, formed the unchanging core of a fighter.
Talk among the students was often sharper. Ryō tried to win debates about technique over Arai. "What I saw from Arai today was awful," Ryō said at one evening meal. "Breathing arts must be precise. Letting the body act spontaneously is a gamble."
Arai looked into his bowl. "A gamble that works when other methods fail," he answered, his tone cold. "If your precision doesn't hurt the enemy, it's just empty precision."
The rivalry wasn't an open quarrel. It was a constant tension. Ryō tried to outsmart Arai in sparring. At one point Arai used his broken breathing to catch Ryō off guard, who had always thought Arai couldn't even reach him. If not for Ryō's absolute underestimation of his opponent, he would have easily taken him many times.
Yet somehow a silence formed between them, built on respect that didn't need to be spoken.
After a few weeks, when the days blurred into a long line of repetition, Arai heard Kenzō, who had stopped by for a short nighttime visit, talking to his kasugai crow. He was near the barn where the birds roosted. Kenzō's voice was low but piercing; still, the words carried.
"Northern mission," Kenzō said softly. "Tomioka is leading. The Water Hashira. Activity is rising. They need reinforcements."
The crow clicked its beak. Kenzō set a small stick on the threshold and wrote a few characters. He sent the bird off.
Arai stood in the shadows and listened. Names with weight lodged in his mind. Tomioka—linked to water—gave him the vague sense that the world, which had seemed distant until now, was closing in on them.
The days then condensed into even denser monotony under the awareness of an approaching event. Kiryuu delivered the message Arai needed to hear: the crow had returned with a reply. Kiryuu untied the scroll, unrolled the paper, and read aloud to the group, without interest—as if he had read it many times:
"Final Selection will begin during the first month of spring on Mt. Fujikasane."
The silence that followed wasn't full of expectation. It was empty and concrete. It sounded like a deadline. Kiryuu turned to his students. "Three months," he said then. "You have three months."
Arai felt no panic, no joy. Only the cold arrival of reality in his chest. Three months. In that number, everything concentrated—training, the daily morning pains, every cough, every sword drill.
Ryō gripped his blade tighter. The others in the room looked at one another. Some nodded. One of them smiled, but the smile faded quickly.
That evening Arai went outside. Snow fell lightly. He stood on a small rise, the wind crossing his cheeks. He held his breath. Blood came from his mouth, ran down his chest, and soaked the bottom of the bandage in dark streaks. His eyes were calm. There was no blaze in them. Only steady intent.
Kiryuu came up and stood beside him. He said nothing. Kenzō stood in the distance with the crow settling back onto his shoulder, stroking its feathers. Ryō was walking back to the stable. The home firelight flickered.
Arai held his breath for a few more seconds, then let it go. The fit didn't come; he managed to hold it in, and it brought unbearable pain.
Only silence. An image meant to remain in memory: a boy who had stopped being just a child, breathing imperfectly, standing firm in winter, blood on his lips, eyes free of needless emotion. In that silence lay a sentence unspoken yet understood by all: time is running.