Demon Slayer: Resurgence

The first light of dawn was not the gentle caress Sumihiko remembered from his childhood bedroom. Here, within the austere walls of the Demon Slayer Corps estate, it was a brutal assault. A sharp, insistent rap on his shoji screen jolted him from a fitful, dreamless sleep. His entire body screamed in protest before he even opened his eyes. Every muscle was a live wire, every joint locked in agony.

"Up. Now." A voice, gravelly and devoid of warmth, sliced through the thin paper screen.

Sumihiko groaned, forcing his eyes open. The tatami mat offered little comfort, and the cool morning air stung his exposed skin. He tried to sit up, a monumental effort that sent jolts of pain through his back and legs. It was only then that he fully registered the figure standing patiently outside his screen, a silhouette framed by the burgeoning light.

His trainer. Master Shiraishi.

The man was old, his hair pulled back in a severe topknot, and his face was a roadmap of deep, weathered lines. His eyes, though, were sharp, piercing, holding an intensity that seemed to see right through Sumihiko's exhaustion. He wore a simple, dark training kimono, and stood with a stillness that spoke of immense, coiled power. He didn't move, didn't utter another word, simply waited.

Sumihiko dragged himself up, swaying slightly, pushing through the nausea of hunger and pain. He was dressed in the simple, rough training clothes provided the night before. His stomach growled fiercely, a hollow ache that gnawed at his insides.

"You have five minutes," Master Shiraishi stated, his voice flat, emotionless, like stone rubbing against stone. "Meet me by the main courtyard gate. Do not be late."

He turned and, with an almost unnerving lack of sound for a man of his build, vanished around the corner of the corridor.

Sumihiko stumbled out of his room, the cool morning air biting at him. The estate was stirring, but silently. He saw a few other figures, cloaked in dark uniforms, moving with an unnerving purpose, but they paid him no mind. The scent of wisteria was sharper now, mingling with the crisp smell of mountain air. He splashed some cold water on his face from a communal basin, the shock momentarily rousing him.

He reached the main gate of the courtyard, his breath already coming in ragged gasps. Master Shiraishi was there, standing with his back to the gate, gazing out at the vast, mist-shrouded expanse of the Okutama mountains. The rising sun was just beginning to paint the highest peaks with streaks of gold, turning the ancient cedar forests below into a sea of deep emerald and indigo. It was breathtakingly beautiful, and utterly merciless.

"Good. You are here," Master Shiraishi said, not turning. "Today, we begin. Your 'athletic prowess,' as Ryuunosuke-sama mentioned, will mean little here. This is not a race. This is survival. This is the path to becoming a blade that can stand against the night."

He finally turned, his gaze fixed on Sumihiko, assessing him with a cold intensity that made Sumihiko feel transparent. "We start with the mountain. You will run it. From here, to the highest accessible point of Mount Mitake. Then back. Without stopping. Each day, you will carry more weight. Each day, you will increase your speed. You will do this until you feel your lungs will burst, your legs will shatter, and your spirit will break. Then, you will run further."

Sumihiko's eyes widened. The scale of the mountain, even shrouded in mist, was immense. To run to its highest point? His mind, accustomed to measured distances and predictable tracks, reeled.

"Do you understand, Sumihiko Kamado?" Shiraishi's voice brooked no argument, no hesitation. "Every fiber of your being, every ragged breath, every ounce of pain will be dedicated to this. This mountain will become your flesh, its trees your bones, its trails your blood. You will know it, intimately. And it will break you, before it builds you anew."

Sumihiko nodded, a tight knot forming in his stomach. He was an athlete. He understood pain. He understood pushing limits. But this felt different. This felt like a complete, utter annihilation of his former self. His muscles were already screaming, his body trembling from the sheer effort of standing.

"Good," Master Shiraishi said, a hint of something unreadable in his eyes. "Begin." He simply pointed to the winding, narrow path that disappeared into the ancient forest beyond the estate's walls.

And with that single word, Sumihiko's new life truly began. He took a shaky breath, swallowed the lump of fear in his throat, and began to run. The cold air burned in his lungs, his legs protested with every step, but the image of Kanata, cold and still in his hidden cell, burned brighter than any sun. He ran for his brother, into the brutal, unyielding embrace of the mountain.

The mountain was a living, breathing entity, its slopes an unyielding adversary. Sumihiko ran. He ran until his lungs burned, a raw, searing inferno with every gasp of the cold mountain air. He ran until his legs felt like leaden weights, each step a testament to sheer, unadulterated will. His heart hammered against his ribs, a frantic drumbeat that echoed the relentless rhythm of his trainers against the uneven earth.

Master Shiraishi was a silent, omnipresent shadow. He didn't run with Sumihiko, but seemed to appear as if from nowhere – materializing at a particularly steep incline, standing impassively at a bend in the path, his piercing gaze a constant, chilling judgment. He never offered encouragement, only the occasional, terse command that cut through the haze of Sumihiko's exhaustion like a blade.

"Faster, Kamado! Your footsteps are too heavy! A demon would hear you from a hundred paces!"

"Focus your breath! Control it! Do not waste energy!"

Sumihiko tried. He forced his mind to focus, to recall every lesson from his track days, every trick he knew to push past the wall of pain. But this was different. This wasn't a sprint, not even a marathon. This was an endless, uphill battle against the very limits of his being, compounded by the constant, heavy ache in his injured back. Sweat stung his eyes, blurring the already indistinct path, but he dared not stop, dared not slow.

They continued upwards, past ancient, moss-covered stone lanterns half-hidden by ferns, past small, forgotten shrines shrouded in mist. The air grew thinner, sharper, carrying the scent of damp rock and ancient forest. The sound of distant waterfalls echoed through the valleys, a mocking reminder of the water he craved.

After what felt like an eternity, Shiraishi abruptly halted Sumihiko at a small, flat clearing overlooking a dizzying drop. The view was breathtaking – layers of mist-shrouded peaks stretching into the distance, painted in the soft hues of the rising sun. But Sumihiko had no mind for beauty. He doubled over, hands on his knees, gasping, trying desperately to pull enough air into his screaming lungs.

"That is enough running for now," Master Shiraishi stated, his voice flat. He pointed to a stack of roughly cut logs, each thicker than Sumihiko's thigh. "Now, you will carry these. From here, to the stream at the base of the next valley. Then back. Fifty times. Without pause."

Sumihiko's head snapped up, disbelief warring with the grim reality. Fifty times? His arms felt like jelly, his back already a burning inferno. He stumbled towards the logs, choosing one that seemed impossibly heavy. He grunted, straining, his muscles screaming in protest as he hoisted it onto his aching shoulder. The rough bark bit into his skin.

"Do not disgrace the Kamado name with such weakness," Shiraishi's voice, sharper now, cut through his pain. "Your ancestor carried greater burdens than logs. Now move!"

The journey down to the stream was treacherous, the log shifting precariously on his shoulder, threatening to throw him off balance on the uneven terrain. The return climb was even worse, his legs trembling with every step, his lungs bursting. He stumbled, falling once, scraping his knee, but he forced himself up, refusing to give in. The sheer, relentless repetition was maddening. Every fiber of his being screamed for rest, for food, for a moment of peace.

Kanata.

The thought was a burning coal in his chest, igniting a fresh spark of defiance. He wouldn't break. Not here. Not when Kanata's life depended on him. His athletic training, the grueling hours of pushing his body to the very edge, had taught him how to endure, how to silence the screaming demands of his muscles and focus purely on the finish line. This was no different. This was just a longer, more agonizing race, with infinitely higher stakes.

He lost count of the trips. The sun climbed higher, beating down on him, then began its slow descent. His body felt broken, utterly spent, yet somehow, miraculously, still moving. There was no 'system' aiding him, only the furious beat of his own will, an indomitable spirit inherited from generations who faced impossible odds. He was a champion, not of the track, but of endurance, driven by a desperate, unconditional love that refused to yield.

As the sun began to dip below the mountain peaks, casting long, eerie shadows through the forest, Master Shiraishi finally spoke. "That is enough for today. Be at the courtyard gate at first light. Do not be late."

He turned and walked away, leaving Sumihiko sprawled on the damp earth, covered in sweat, dirt, and the residue of shattered limits. Sumihiko lay there, gasping, trembling, every inch of him screaming. But even through the pain, a small, defiant flicker of determination remained. He had survived the first day. The mountain hadn't broken him. Not yet.

The morning broke with the same ruthless efficiency as the previous day. Sumihiko woke to the familiar, sharp rap on his screen, his body stiff, every joint screaming in protest. The brief, restorative sleep had done little to mend the utter depletion of his reserves. His muscles, bruised and torn, felt like a tangled knot of pain. But Master Shiraishi's silent presence by the courtyard gate, his gaze a relentless pressure, left no room for complaint.

"Run," was the only command. And Sumihiko ran. He ran the same punishing mountain paths, the cold air scraping his throat, his legs burning, his lungs pleading for oxygen. He carried rough-hewn stones in a weighted backpack, the added burden a constant reminder of his physical inadequacy, despite his lifetime of athletic conditioning. Each ascent was a battle, each descent a treacherous test of his trembling knees. The majestic beauty of the Okutama peaks was utterly lost on him; all he saw were obstacles, endless, unyielding.

After hours that stretched into an eternity, Sumihiko, gasping for breath, found himself abruptly halted by Master Shiraishi in a secluded hollow deeper in the mountain. The air here was cooler, tinged with the scent of damp earth and ancient stone. And then Sumihiko saw it.

It rose from the earth like a primordial beast, a gargantuan mass of dark, weathered stone. Its surface was pitted and scarred by time, streaked with moss and lichen, but its sheer scale was breathtaking, utterly overwhelming. It dwarfed the surrounding cedar trees, casting a long, imposing shadow. It was an impossible, insurmountable leviathan.

Sumihiko's breath hitched. He had heard the stories, of course. Whispers of his ancestor, Tanjiro Kamado, and the almost mythical feat of slicing a massive boulder to pass his training. But this… this was far grander, far more daunting than anything he had ever imagined. This boulder seemed to mock the very idea of a human blade touching its surface, let alone cutting it.

Master Shiraishi stood before the immense stone, his posture unnervingly calm, his eyes fixed on Sumihiko. "This," he stated, his voice flat, devoid of emotion, "is your final test. Your gateway to the Final Selection. Until you can cut this boulder in half, you are not worthy to stand among the Demon Slayers."

He paused, letting his words sink in, the cold, impossible truth of them. "It is larger than any boulder cut before. A challenge befitting your lineage, Kamado. There will be no further guidance on this task. When it is split, you will be ready."

Sumihiko stared at the boulder, a cold dread seeping into his bones. It was a joke, a cruel, impossible jest. How could a human, with a mere sword, cleave such an immense, unyielding mass? His mind screamed in protest. His athlete's pride, usually a wellspring of confidence, crumbled into dust before the sheer, unmoving indifference of the stone.

Master Shiraishi then produced a heavy wooden sword, a bokken, from behind his back. Its lacquered surface was smooth, cool against Sumihiko's sweat-soaked palm. "Now, the blade."

He began with the absolute basics. "Grip. Stance. Weight distribution. Focus." His instructions were terse, precise, delivered with an almost brutal efficiency. Sumihiko, despite his innate athleticism, felt utterly clumsy. He had spent his life honing his body for speed and power, for explosive bursts of energy. The sword demanded something entirely different: balance, precision, a fluid, almost meditative control.

His first swings were a disaster. The bokken felt like a foreign object in his hand, awkward and unwieldy. He swung vertically, his muscles screaming, trying to put all his raw strength into the strike, but the blade wobbled, his stance was off, and the impact, when it came, was a jarring, painful vibration up his arms. It felt incredibly ungraceful, a pathetic flailing compared to the elegant, deadly dance of a real Demon Slayer.

"Useless!" Shiraishi snapped, his voice a whip-crack. "Control your power! Guide the blade! You are a dancer, not a lumberjack!"

Sumihiko gritted his teeth, sweat stinging his eyes, mixing with the dust he kicked up. He swung again, and again, and again. He tried to follow Shiraishi's terse commands, to adjust his stance, to channel his strength through his core. But the sword refused to cooperate, feeling heavy and clumsy, a testament to his new and profound ineptitude. He was good at running, not this. He was an athlete, not a warrior.

This is impossible, a voice whispered in the back of his mind. You can't do this. You'll never cut it. You'll never get Kanata back. The image of Kanata, confined behind that heavy, sealed door, was a cold, sharp pang in his heart. The immense boulder loomed before him, an unyielding monument to his current powerlessness. He swung again, a desperate, clumsy arc, the bokken whistling uselessly through the air. The mountain remained silent, a stoic witness to his burgeoning despair.

Days bled into a relentless, agonizing cycle. Sumihiko's life became a brutal symphony of pain and repetition. Every sunrise brought the same cold command from Master Shiraishi, the same grueling climb up Mount Mitake, the same bone-jarring sprints through the ancient forests. Then came the hours with the sword. Strike. Pivot. Breathe. Strike again. Each swing of the wooden bokken was a testament to his utter lack of grace, his inability to marry his raw athletic power with the fluid precision Master Shiraishi demanded.

"Your posture is weak! Your grip is uneven! Your focus drifts like autumn leaves!" Shiraishi's voice, always flat, always sharp, cut through the mountain air, each correction a fresh lash to Sumihiko's already raw pride. The immense boulder, his impossible target, stood as an unmoving monument to his failure, mocking his every clumsy effort. He would swing, envisioning the cleaving cut, only for the bokken to whistle harmlessly through the air, its blow absorbed by nothing but his own frustration.

The physical pain became a dull roar, a constant companion. His hands were a mass of blisters and calluses, his muscles screamed from dawn until his exhausted collapse at night. But far more insidious was the mental strain. He was Sumihiko Kamado, the fastest runner, the one who always pushed harder, who always found a way to win. Now, he was inept. A failure. He couldn't even manage a proper sword swing, let alone begin to fathom the elusive 'Total Concentration Breathing' that Shiraishi hinted at, a concept as vast and intangible as the mountain itself.

This is pointless, a voice, cold and despairing, whispered in his mind as he collapsed one afternoon, sweat plastering his hair to his forehead, his bokken clattering uselessly to the ground. You're not doing anything. The boulder isn't even chipped. Kanata is still locked away. You're failing him. He thought of his old life, the roar of the crowd, the satisfying burn of a sprint that led to triumph. Now, there was only this endless, agonizing struggle, with no finish line in sight.

He lay there, gasping, staring up at the impassive face of the boulder. It was bigger than Tanjiro's. Too big. An impossible task given to a boy who knew nothing but how to run. What was he doing here? He felt a desperate urge to simply give up, to curl into a ball and let the mountain swallow him whole.

Then, a different image burned through the haze of his despair: Kanata's small, still face, framed by the rough blanket in his confinement. The single tear that had fallen on his own hand. The desperate, silent plea that fueled his entire, impossible journey.

"No," Sumihiko choked out, forcing the word past his burning throat. "No, I won't. I can't." He squeezed his eyes shut, clenching his fists. I promised you, Kanata. I promised I'd bring you back. I can't give up. Not now. Not ever.

He pushed himself up, grunting, his body protesting every inch of movement. His muscles trembled, but they obeyed. He picked up the bokken, its familiar weight a testament to the countless repetitions he had already endured. He brought it up, his stance still awkward, but perhaps, infinitesimally, a fraction more balanced than yesterday. His arms, though screaming, swung a tiny bit more smoothly. And when he focused on his breath, there was a fleeting, almost imperceptible moment where the scattered threads of his thoughts seemed to pull together, a spark of clarity amidst the chaos.

He didn't notice these tiny improvements. He only felt the overwhelming pain, the crushing frustration, the seemingly insurmountable distance between him and the unyielding boulder. But somewhere, deep within him, beneath the layers of exhaustion and despair, something was shifting. The constant, brutal pressure was slowly, agonizingly, reshaping him. He was a stone, slowly being honed by the merciless river, unknowingly sharpening into a blade. And the mountain, his silent, demanding master, watched.

The ceaseless, punishing rhythm of training had long since ceased to be an external force. It was now a part of Sumihiko himself, a constant, low-grade hum of pain and exhaustion that defined every waking moment. The days blurred into a monotonous, brutal grind of mountain running and sword practice, each swing of the bokken a testament to his persistent frustration. He had tried to simply will the boulder to yield, using the raw, explosive power of his athlete's body, but the stone remained indifferent, and his technique remained clumsy.

One late afternoon, amidst a grueling session of endurance swings, Sumihiko's mind, battered by fatigue, faltered. He swung with a ferocious yell, putting every ounce of his remaining strength into a vertical cut, his form sloppy and off-balance. The bokken wobbled, the intended "cut" a clumsy, horizontal arc, and his footing, lost to a moment of uncontrolled energy, gave way. He stumbled, falling hard onto the mossy earth, the bokken flying from his grasp. The jarring impact sent a fresh wave of agony through his back.

He lay there for a moment, panting, the cold despair threatening to consume him entirely. He had fallen. He had failed. A useless, clumsy, pathetic failure. The boulder loomed in his vision, a massive, unmoving symbol of his inadequacy.

"You waste your life," Master Shiraishi's voice, quiet and unwavering, cut through the silence. Sumihiko, embarrassed and exhausted, pushed himself up onto his elbows. The old man stood over him, not with anger, but with a profound, weary sadness in his eyes.

"The blade is not a club, Kamado," Shiraishi continued, his words slow and measured. "You see your strength as a force to be unleashed. But the sword is a tool of precision. It is a razor's edge. A razor cannot be forced through stone. It must be guided. Its power comes not from the force of your arm, but from the focus of your core, the control of your breath, the stillness of your mind. You will never cleave that stone with brute force."

He gestured to a small, intricate pattern of cracks on the bokken lying on the ground. "See this? The blade has a path. A purpose. You must find it. You must become a river, not a flood."

Sumihiko, his mind still reeling from exhaustion, listened. The words, unlike the previous terse commands, resonated with a deeper, more profound truth. He had been trying to run through a wall, when he should have been looking for the door. He had been trying to beat the boulder into submission, instead of finding a way to master it.

Slowly, painfully, he picked himself up. He retrieved the bokken, its familiar grip now feeling different, not just a heavy piece of wood, but a tool waiting for purpose. He stood before the boulder, not with anger, but with a new, quiet focus. He closed his eyes, forcing his breathing to slow, to become deeper, more deliberate. He inhaled, imagining the air flowing not just into his lungs, but through his body, down into his core, a well of focused energy.

He opened his eyes. He raised the bokken, not with the intention of destroying the stone, but of guiding the blade. He ignored the screaming protests of his muscles and focused on a single, clean line down the center of the boulder's face. He began to swing, slowly at first, then with building speed. He didn't put his strength into the swing; he put his control into it. He focused on his breath, on his form, on a clean, perfect arc.

And then, for the first time, it happened. His swing, though still lacking power, felt clean. Precise. The bokken sliced through the air with a faint, perfect whoosh, its path a flawless vertical line. His stance, for a fleeting, beautiful moment, was perfectly balanced, his feet rooted to the earth, his core engaged. He felt the focus, the stillness, the quiet power of a controlled movement. It was not the clumsy, chaotic flailing of an athlete, but the first, delicate stirrings of a swordsman's grace.

He didn't make a sound. He didn't even realize he had done it until the swing was over. He just stood there, breathing, his heart pounding with a different kind of intensity. Not of exhaustion, but of profound, bewildered hope. The boulder was still there, untouched, unyielding. But his perception of it had changed. It was no longer an impossible monument to his failure. It was a challenge, immense and daunting, but now, for the first time, he felt that he might just be capable of meeting it.

The days that followed his small breakthrough were a paradox of immense exhaustion and newfound purpose. Sumihiko continued his brutal regimen of mountain runs and strength drills, but now, his time with the sword was no longer a fruitless battle against his own ineptitude. He focused on the feeling he had discovered, the silent, concentrated power of a perfectly executed cut. He practiced endlessly, finding the elusive balance between form and force, and slowly, agonizingly, the clumsy, desperate swings of the athlete gave way to the first, disciplined motions of a swordsman.

His breathing, too, began to bend to his will. The concept of "Total Concentration Breathing" remained impossibly difficult, but he could now hold it for a few seconds at a time, feeling the surge of energy, the heightened focus, before his concentration inevitably broke. He was no longer just flailing; he was learning. He was growing.

One evening, as the last rays of sunlight bled through the dense forest, painting the ground in a mosaic of gold and shadow, Sumihiko stood before the boulder, practicing his swings. He was drenched in sweat, his arms trembling, but his posture was straight, his grip firm. He completed a set of ten vertical swings with a precision that would have been impossible a week ago.

"Good," Master Shiraishi's voice came from behind him, startling Sumihiko into a rigid stance. The old man had been a silent observer for the past two hours, a stoic shadow in the fading light. He walked to Sumihiko, and for the first time, his eyes held something other than cold scrutiny. There was no smile, no praise, just a simple, concise acknowledgment of his progress.

"Your foundation is solidifying. You have stopped fighting the mountain, and have begun to learn from it," he said, and Sumihiko felt a warmth spread through his chest that had nothing to do with the setting sun.

Shiraishi then produced two different objects. The first was a sheathed katana, its scabbard a simple, polished black wood. The second was a thick, bamboo reed, a green, living thing that had been cut clean and stood almost as tall as Sumihiko.

"You have learned to swing with a wooden sword," Shiraishi stated, handing Sumihiko the katana. "Now, you will learn to cut with a steel one." He drew the blade just enough to reveal a sliver of its edge, a cold, glittering line of lethal precision. "Its weight and balance are different. Its purpose is to slice, not to smash. The slightest imperfection in your form will shatter the cut."

He pointed to the reed. "You will start here. Do not try to chop it down. You must cut it so cleanly, so swiftly, that the top half slides from the bottom without falling over. That is the first measure of a true blade."

Sumihiko, his hand trembling, took the katana, its hilt cool and alien in his grasp. The weight was different from the bokken, the balance more subtle. The thought of this lethal edge in his hands was both thrilling and terrifying. His training had just entered a new, more dangerous phase.

He stood before the reed, then looked past it, to the massive, unyielding boulder. The stone was still there, untouched. Master Shiraishi had not mentioned it, had not even glanced at it. Sumihiko understood now. The boulder wasn't his immediate opponent. The boulder was the final exam, the ultimate destination he was still months, maybe years, away from reaching. All of this – the grueling runs, the sword drills, the control of his breath – was merely the path leading to it.

He took a deep breath, focusing, trying to settle his mind, his eyes fixed on the simple, green reed before him. The mountain air, cold and unforgiving, filled his lungs. He was no longer just a boy trying to survive. He was a Slayer in training, and his journey had only just begun.