Chapter Text
It started with dreams. Nightmares so vicious that they sunk their claws into him well into the waking hours. In those dreams, his hair was longer and his skin marred with scars that traced every inch of his skin. There were also the screams, long and anguished and he couldn’t tell if they came from him or someone else, only that they rang out for what felt like forever.
There were multiple nightmares that took turns tormenting his restless nights. But the one that haunted him most was one that took place in a lantern lit hellscape. Constructed of tatami floors and traditional wood paneled walls ceilings, it shifted and thrummed to the sound of a biwa, each strum filling him with an indescribable terror he couldn’t place. Katsuki sprinted with urgency, tearing through horrible creatures with a sword and expert precision as he tried to reach something he couldn’t remember. Sometimes, there were others with him, sometimes he was alone. The figures of other swordsmen flitted around him in graceful glimpses, always too fast to see clearly. He trusted them, he thought, but Katsuki’s focus was on something, someone else who hovered on the edge of recognition. He always woke up before he could reach them anyways.
When he woke up, his sheets were soaked with sweat, an explosion waiting to happen whenever he returned to the waking world. And every time he would gather his ruined bedding and creep downstairs to wash it as quietly as possible. He was going to be a hero for crying out loud, no way he was going to tell anyone he had recurring nightmares, that was for babies.
Maybe that’s why he got into the habit of being an early riser, an unusual one for a middle school boy. He was eleven, but with an exhausted regularity, he woke up around four AM to start his day. That also led to him going to sleep around eight for any attempt at rest before the nightmares started again. The fear and adrenaline flooding his system every morning left him restless and angry, so he took to exercising first thing in the morning.
It frustrated him at first, the way his arms shook and collapsed under the pressure. Sweat beaded and pooled on his skin in a way that felt demeaning instead of empowering like when he used his quirk. Somehow, in the wee hours of morning when he was trying to work out what was definitely not fear from his frantic brain, he felt calmer. It still pissed him off to no end how his body refused his will like the way it used to, but he only resolved to become stronger in spite of it. What he felt by his body not behaving how it should, he rationalized by his familiarity with his quirk obeying him more than his scrawny muscles did.
So for months this became his routine: wake up from his fitful sleep, train until he could barely move, take care of his morning tasks, and lie down in bed for his mother to wake him up as if he never left the bed. Did Katsuki ever wonder if she suspected anything? Yes, but he figured if she did know, she didn’t object. Begrudgingly, he became a little bit nicer after adopting his new habit, if only somewhat. Not that he would ever admit to such a thing, but he even started being slightly less aggressive towards that shitty nerd Deku. Katsuki still wouldn’t admit he tolerated him, but he did bite a kid's head off for knocking the nerds books over. Whatever, it still wasn’t like they were friends or anything. And if Deku smiled at him like he hung the stars after that, then well Katsuki wasn’t going to say anything about that either.
But the nightmares didn’t stop. Even as he was halfway through middle school and considerably more muscular than most of his peers, they didn’t cease. His nights only became more intense, more vivid. The figure that used to dance on the edges of his vision came into clear focus now. Sharp eyes and sharper blades danced around him as the version of him in the dreams fell into graceful pace with them. Their names were on the tip of his tongue, but whenever he felt like he almost remembered, he woke up.
In tandem with the worsening dreams, his workouts became more intense. Using his quirk never seemed to help with the building terror that came from being still, so he begged his parents for a wooden sword and lessons. They had looked at each other with confusion evident on their faces, but signed him up anyway. It may have been an odd request, but if it kept their son out of trouble and away from exploding anything that existed wrong near him, then who were they to ask questions. So from then on, he traveled to a rural workshop three times a week after school to learn sword fighting. He picked it up fast of course, he thought, because Katsuki was good at learning anything. But even then, the tension under his skin only grew. After the first lesson, he had the worst nightmare he had seen yet.
He fell into the weird hellscape again, hands gripped tightly around his sword as the wind whipped his hair and clothes around. This time felt different, more real, as Katsuki fell. It felt less like a dream and more like a memory. When he finally landed, he was the one fighting. It no longer felt like he was floating, merely spectating his own body, but like he was truly there. The sting in his muscles felt dull as if he had experienced it a thousand times before, yet fresh as if it was Katsuki’s own body. All his senses were alight with input, telling Katsuki everything he needed to know. The slayers he fought with were sharp and strong in his mind, as easy to recall as breathing. And wait, since when did he know any of these guys, much less what a slayer was? His head pounded with the conflicting memories. Even his name didn’t feel right anymore as his body moved and fought on its predetermined path it took every night.
The blur of blood and steel dizzied and exhilarated him through the fight. As he drew to the end of his dream, the people he fought with came into view as well as a horrible thing. It looked like a man, but so awfully wrong. It had six crimson eyes and moved so fast he felt his heart stutter as the thing attacked. ‘Kokoshibo’, his brain was supplied against his will. He did not want to remember what this abomination was, if it truly was a memory. But unfortunately, the dream did not end like it should have already. And Sanemi, ‘who was Sanemi?’ Katsuki wondered, prepared himself to attack.
The fight seared itself into Katsuki’s brain, embedding itself into his mind as blood and limbs flew around him. But the worst was yet to come, as it always was. The someone he was trying to reach finally freed himself from the fog in his mind.
———
“GENYA!” Sanemi sobbed, cradling what was left of him. His tears fell and sizzled on the burning body of his brother, wetting the ash becoming him and mixing with his brother's own blood. His thumbs swiped under brothers eyes, attempting to wipe away the onslaught of tears. Gurgling erupted from his little brother's throat as he tried to speak, but the words wouldn’t form, stopped by the blood drowning his vocal cords.
The tears fell harder from his eyes, blurring his vision as he pulled Genya tighter to his chest, as if to delay the inevitable. “PLEASE DON’T TAKE HIM! Please…” his voice came out in broken gasps. “I love you Genya, please, please don’t leave me too!” Sanemi begged. He stroked the top of his brother's head, desperately trying to stall the way it began to crumble under his fingers. Genya's eyes locked with him and for a moment it felt as if time stopped. His brother’s, his baby brother’s, lips attempted to form a sentence but the fangs protruding from his teeth made it a struggle. Sanemi cupped his face in his hands and kissed his forehead, feeling his tears slide off his face and onto Genya’s. Quietly, far too quietly for the loud force of nature that was his baby brother slipped the words.
“I-I… love you-u… Nemi. My N-Nemi is the nicest… person… i-in the… whole…wo…” the words cut off at the end, the blood spilling from his lips stealing his last words from him.
Sanemi clutched him tighter. “I love you too baby, I love you so much, I’m so so sorry” he cried in anguish. The last of his brother crumbled under his palms and he howled. The screams shook his entire body, pulling his heart apart as if he might die and join his brother as well. It only stopped when a large hand was placed on his shoulder. He turned to see a face washed clean of blood and ash by rivers of tears pouring down from unseeing eyes. “Come, Shinazugawa.” Himejama said. “There is nothing left for us to do, but fight, and ensure young Genya did not sacrifice his life in vain.” He said calmly, but anger lay behind his words. For the first time, the rage Sanemi felt was mirrored in his mindful colleague. Sanemi rose, watching the ashes blow away in a strange wind, before following the older, hands steadied in anger.
———
That morning, Sanemi woke up. His hands gripped the sheets and his breath came out in harsh blasts, but the worst part of it all was the memories. Everything came flooding back to him at once, a whole lifetime of pain in an instant hitting him like a truck. For long minutes, he rocked back and forth, trying to stop the tears and snot and sobs. When he finally calmed down enough, he tugged on his sweats and a black hoodie and went for a run. He let the icy air purge his senses as he wracked his mind for how two lifetimes of memories were coexisting in his skull. His feet hit the ground harshly as he let his body carry itself through the woods surrounding his house. How? How? He had no idea.
Obviously, he was Katsuki Bakugou, 13 years old and possessor of an explosion quirk. But at the same time he remembered all 25 years of Sanemi Shinazugawa, the Wind Hashira. It was a new body, a new life, yet at the same time it felt like an extension of an old one. He certainly didn’t feel 38 years old, he felt thirteen, but he also felt the same way he did as a 25 year old. It was so confusing! He let his feet carry him through the dark woods, the hour being much earlier, almost two AM, compared to his usual wake up time. Sanemi-Katsuki, turned his focus to running until he could think again. Hell, he didn’t even know what name to think of himself as anymore.
Eventually, his feet slowed down as he approached a roaring waterfall in the woods. Katsuki had never been here before, but Sanemi had. It wasn’t one he used to frequent, rather one he had encountered a few times on mission, but he figured it would do the trick. He stripped down to his boxers, neatly folding his clothes and setting them on a nearby rock. He ignored the way his body suddenly felt wrong, looking at the smooth and scarless expanse of his less muscular chest. Slowly, he waded through the water until he reached the base of the waterfall. Foam and spray splashed him and threatened his vision, but he just methodically crawled atop a smooth stone emerging from the water under the strongest part of the falls, and closed his eyes.
He felt his posture stiffen as the freezing water pelted down on him, but he forced his spine straight and his hands into a praying motion. A normal child would’ve been knocked aside by the power of the water, but Katsuki was Sanemi, a Hashira. Of course this new body wouldn’t last as long as his old one, but he would be able to last until almost daybreak before starting his training. Katsuki was nearly clueless around a blade, but now that he remembered who he was, it wouldn’t be terribly difficult to relearn everything he could do in his past life.
The real question was whether or not he would fight demons. His dream had been to be a Pro-Hero after all, but now that he remembered everything he wasn’t so sure anymore. The memory was fuzzy, and Sanemi couldn’t quite see it clearly, but he remembered how he died. He had expected to go peacefully in his sleep, just as Giyuu had, but instead he had been killed on the eve of his 25th birthday. Weakened by the curse of the demon slayer mark, there was nothing he could do to prevent his death by the one thing the world had thought they were free of: a demon.
It was Muzan, because of course it was. Of course he couldn’t have gone down that easily. He had been crippled, nearly turned to dust, but somehow he had survived. A piece of his body had been kept hidden somewhere was what the bastard had said.
“It took absolutely forever to regenerate, even I had started to lose hope, but I’m back now Hashira.”
And Sanemi had been killed. It wasn’t surprising, the Corp had been all but disbanded, all the other Hashira dead and the last one dying. Of course he would have been killed. It made Sanemi sick.
This was a new life, a chance to be free from the war he had died in. But the way he had felt his brother crumble to ash under his own hands inspired another idea. He was going to kill that fucker, or die trying. Katsuki could be a Pro-Hero once Sanemi got his revenge. The water started to heat up around him as his anger grew, but the speed of it washed away any sweat that got the chance to form on his palms.
As daylight crept over the treetops, Sanemi pulled himself from the waterfall and picked up his sword. He had the advantage this time around: experience. And this time, he would be the greatest, not for himself, but for his brother.
———-
The months fell by in the same pattern. The Katsuki everyone knew would go to school, learn, use his quirk and show off a little bit. There was never a suspicion of anything more to the boy. The extra muscle mass could be explained away as part of his dream to become a Pro-Hero. The change in attitude, becoming a touch colder but significantly less explosive was waved away as maturity. Katsuki even started to be halfway friendly to Deku. He still refused to actually call them friends, but he made an effort to stop being an active jerk to him. He didn’t know why specifically he stopped pushing him away so hard at first, but after another nightmare, this time of a fight with Genya, he understood it. Even if couldn’t admit to himself that he was friends with the other boy, he refused to hurt someone the way he hurt Genya again.
But whenever he went home, he felt more like a demon slayer than a boy again. His training snowballed into something as insane as what he put himself through in order to become a Hashira. Even with just a wooden sword, he picked wind breathing back up again with startling ease.
Eventually, he was able to track down what was left of the corps, and found that they were still running, if discreetly. Since demon slayers were primarily quirkless, it was easy for the organization to fly under the radar since the government was too busy trying to farm actual heroes. The resurgence of Muzan led to a new wave of demon activity, calling forth new generations of slayers. None, he had discovered, developed the mark since his own generation had passed. There was also a distinct lack of Hashira, as the lack of guidance since the corps had more or disbanded after Muzan’s “death”, and had been struggling since. They did, thankfully, still have a final selection.
Sanemi signed himself up for final selection under the guise that it was a summer camp to his parents. They were just happy he was finally behaving himself and didn’t ask any questions. Deku had wanted to go too, but Katsuki evaded any and all questions about it until the nerd finally gave up. Even if he was being somewhat nice to him didn’t mean he wished his friend an early death at 14.
The only problem left was a nichirin sword. Luckily, he knew where to find one. And if that meant grave robbing his own grown-over tomb, then it wasn’t really stealing, was it?