The blade cuts through the air. It was dark. No stars visible. The moon hidden behind clouds. Halfway up Mizugaki Mountain, in the darkness before dawn, Rengoku Kyojuro continued swinging his sword alone. Flame Breathing, First Form—Unknowing Fire. The blade of his Nichirin sword turned a pale crimson. Forged from scarlet-crimson iron sand, the blade sensed the blood of one with affinity for Flame Breathing and grew warm in response. A special resonance granted only to those who wielded flame. Second Form, Third Form, Fourth Form followed in succession. With each form layered upon the last, the redness of the blade deepened, and heat began to ride upon the slashes that tore through empty space. Kyojuro's breathing remained steady. The foundation of the breathing technique mastered by Demon Slayer Corps members—raising the oxygen in one's blood to its limit, elevating physical ability beyond human limits. He maintained that sensation constantly while chaining the forms together. Fifth Form, Sixth Form, Seventh Form, Eighth Form. The sword sang. The withered grass at his feet trembled from the aftermath of the slash. And then—Ninth Form. Kyojuro drew in a deep breath. Pouring everything into it. The Secret Technique: Purgatory. The culmination of Flame Breathing passed down through the Rengoku clan. The blade began to turn a vivid red. Heat was coming. Coming— It scattered. The heat dissolved into the air and vanished. The blade's radiance faded as if it had been a lie. Only silence remained. This was the hundred and thirtieth time, Kyojuro counted silently in his heart. It was not impatience. He had moved beyond that stage long ago. What remained was something heavier, something that accumulated quietly with each passing day and now settled at the bottom of his chest like stone. Unmovable. (It should not be a matter of technique.) Even questioning everything from the beginning, the answer did not change. From First Form to Eighth Form, his movements held no flaw. His breath control was sound. The trajectory of his blade maintained the correct form that Aoba had beaten into him. And yet, the Ninth Form alone scattered into mist like this every single time. He returned his sword to its sheath. Slowly. In the darkness, only the outline of the small house was visible. A simple structure of six-mat rooms and a dirt floor—the kind the Rengoku clan had used as a training ground for generations. In that small house built halfway up this mountain, Mizugaki Mountain, at an elevation of roughly eight hundred meters, Kyojuro had spent eight months with Aoba. When he pulled open the door and stepped inside, the smell of time soaked into the dim interior greeted him. Worn tatami mats. Scorch marks on the pillar—from when Aoba had tried to demonstrate a form of Wind Breathing here instead of at the training grounds, and her slash had grazed the wood. A Nichirin sword leaning against the wall. On the shelf above, the medicine box Aoba had brought sat in place. Several bundles of medicinal herbs tied with thin cord were arranged beside it. Aoba was not here now. She had said she would return at dawn. Kyojuro wiped away his sweat and drank a cup of water. When he raised his eyes from the cup in his hand, the medicine box on the shelf entered his field of vision. He deliberately looked away. He understood the reason well enough, and precisely because he did, he avoided thinking deeply about it. —His feelings toward Aoba. He certainly respected her. Two years ago, when Kyojuro had passed the Final Selection and joined the Demon Slayer Corps, it was Aoba who had offered him her training grounds. She wielded Wind Breathing—a variant she had independently derived from Wind Breathing—and continued to set an example as a senior swordsman. But there was something more than that. What that something was, Kyojuro had not yet named within himself. Deliberately, he avoided naming it. If unnecessary emotions crept in during a mission, judgment dulled. That was the code of a Demon Slayer Corps member. Aoba understood that better than anyone. Which was precisely why he could not let her see through him. Kyojuro raised his face and turned his gaze toward the instruction manual on the shelf. The record of Flame Breathing passed down through generations of the Rengoku clan. A cover worn to tatters, pages bearing the marks of countless readings. He had heard that his father had damaged part of it during a drunken episode. Only fragments of the description regarding the secret technique remained. Kyojuro took the manual from the shelf and opened to the page of the Ninth Form. A familiar passage lay there. "The Ninth Form is not a technique. It is the flame of the soul itself. A realm forever beyond the reach of those who possess nothing to burn." With each reading, these words grew heavier. Not a technique. The flame of the soul. Something to burn—. (What is there to burn?) He could not understand. If it was not technique, then what was it? What should he burn? Emotion? Resolve? Or his own life itself? He continued to question, but no answer came. Eight months of swinging his sword on this mountain had not yielded one. He closed the manual. Outside, the sky was beginning to lighten. Dawn. --- The sound of wings beat against the eaves. A heavy sound. Not an ordinary bird. Kyojuro knew before he even pulled open the door. When he stepped outside, a large black bird was perched on the eaves of the small house. A Kasugai Crow—a messenger bird used by the Demon Slayer Corps. Faster than government telegraph, cutting through mountain passes with the Corps' own unique communication network. The bird cried out in a sharp voice. "[serious]Hotarubi Village! Multiple Demon Presences! Highest Alert! Sortie Immediately!" The crow spoke only those words before taking flight into the darkness. Kyojuro let the words roll through his mind for a moment. Hotarubi Village. Roughly sixty kilometers west of Mizugaki Mountain, positioned through mountain paths—a small settlement. Its population was fewer than eighty, people who lived by charcoal burning and gathering mountain vegetables. When night fell, it was wrapped in complete darkness—a good hunting ground for demons. But that was not the problem. "Multiple demon presences." That was what was strange. In his two years as a Corps member, Kyojuro had been drilled in demon habits. Demons held territories. They acted alone. Multiple demons gathering in the same place was ordinarily impossible. The predator's instinct prevented it. Multiple gathering in one village—that was no coincidence. Something was gathering the demons. The hierarchy of the Demon Slayer Corps flowed through Kyojuro's mind. Ten ranks from lowest to highest. Roughly three hundred members guarded the darkness across Japan. At the apex stood the Pillars—nine in total, the highest-ranking swordsmen who had each mastered a different breathing technique. Led by the Ubuyashiki clan as the organization's head, only the Pillars held command authority over their assigned territories. To become a Pillar, one had to either defeat a member of the Twelve Kizuki or slay fifty or more demons. Ten days remained until the Pillar Trials. (Forty-three.) His current demon count. Seven more would meet the requirement. If this mission involved multiple demons, there was a possibility of fulfilling the remainder—but Kyojuro stopped his thoughts there. He did not understand why multiple demons would gather. That uncanniness canceled out his calculations. He began to gather his belongings. Inspection of his Nichirin sword, checking the blade's condition. When he pulled his haori—the black uniform with red trim—over his shoulders, his fingers brushed his left shoulder. There was a small burn scar there. A wound he had inflicted on himself early in his training when he had made an error in a Flame Breathing form. When Aoba had taken out salve from the medicine box, she had laughed while saying, "You're too hasty." (…Don't think unnecessary things.) Kyojuro tightened his consciousness. He pulled the carrying cord taut and returned the manual to the shelf one last time. The answer to the Ninth Form was not here yet. Kyojuro still did not know what there was to burn. He placed his hand on the door. The fact that this would be a mission with just him and Aoba surfaced in the corner of his chest, and in that moment, Kyojuro consciously pushed it down. He could not let his senior see through him. He could not dull his judgment by bringing unnecessary things into this. The sound of the door closing was swallowed by the morning stillness of the mountain. --- Morning mist hung over the old path down the mountain. A stone-paved road winding through a mountainside of mixed cedar and pine. Kyojuro pressed his feet firmly against that road, unchanged since the Edo period. The stones beneath his feet were damp, and each time the mist touched his skin, it was cold. From a distant valley, a thin column of cooking smoke rose. Morning in some village. An ordinary morning was coming for someone, their daily life. The average lifespan of a Demon Slayer Corps member was short. Only about twenty percent of members survived five years or more. When Kyojuro had joined, there were twelve in his cohort. Seven still lived. Five had died in two years. He knew all their names. He knew all their faces. Fellow survivors of the Final Selection on the same mountain—Fujikasane Mountain, within the wisteria flower barrier. (If I cannot become a Pillar—) That thought, if continued, would roll in an unpleasant direction. Aoba's eight months would become meaningless—that fear pooled at the bottom of his heart. She had invested her time in him. She had accompanied him through morning training sessions, correcting each flaw in his forms one by one, standing silently beside him during the breathing cultivation at Shiranui Waterfall. Kyojuro knew the full weight of all of it. So he had to become a Pillar. That was the answer. There was no other meaning to these eight months. In the mist, a small bird took flight from a nearby branch. The sound of its wings striking the air seemed oddly loud. Kyojuro's eyes followed it instinctively, but the bird disappeared into the mist beyond. Halfway down the mountain path, an old stone Buddha lay half-buried in grass. A small stone deity with a laughing face, and someone had left a single wild chrysanthemum before it. (Does anyone pass through here?) Thinking such things absently, Kyojuro walked on. Someone who did not know of the Demon Slayer Corps had passed through here during an ordinary journey and left a flower at this stone Buddha. That kind of daily life existed on this mountain too. What needed to be protected was such places. Only the sound of his feet on the stone path continued. --- Evening was approaching. Since entering the highway that stretched west from Mizugaki Mountain, the color of the sky had begun to change. Beyond the cedar forest, the light was turning orange. Perhaps another ri or so to Hotarubi Village. Kyojuro opened his nasal passages as he walked. Something was mixed in the wind. At first it was faint. But it was certainly there—the smell of something rotted. Blood and decaying flesh—something alien, not beast nor human. That smell a Demon Slayer Corps member's body learned to react to instinctively. Not just one. Kyojuro stopped walking. He stood motionless in the middle of the highway. He drew in the breath of Total Concentration, sharpening his senses. Three. Four. As he counted, it seemed to increase. Five, six. Perhaps seven or more—in the depths of the cedar forest, in the darkness where the color had faded with dusk, something was moving. The presence was unmistakable. This was wrong. Demons did not move until the sun set. Sunlight killed demons. So demons emerged at night. There was no reason for a presence before sunset. An