So I saw Mugen Train MONTHS ago with my wife and ever since Rengoku has been my guy. My wife now refers to him as my husband, I aint even mad about it, in the course of a single movie he secured his position on my Mt Rushmore of Anime characters. Enjoy.

Disclaimer: I do not own RWBY or Demon Slayer or any of their characters. This a fan made story written purely for entertainment and nothing else. All credit goes to the respective owners.

"RENGOKU!" He heard the muffled scream of Tanjiro over the deafening thumps of his heart in his ears, he pushed it all out of his mind as he focused all of his strength into his grip on the demon arm currently in his gut.

"Just... a bit... longer." He whispered as Akaza struggled to free himself.

"LET GO!" Akaza shouted as he pulled harder without success, a small light began to shine just over the horizon igniting even greater panic in the demon. "YOU FOOL, BECOME A DEMON AND WE CAN BOTH LIVE!" He screamed at the Hashira. "RENGOKU!"

Rengoku smiled despite the extraordinary pain wracking his whole being. "I'm... sorry... Akaza." Every word was a struggle, blood leaking out of his mouth. "You... were strong... a true... warrior. Let us... go... together."

The upper third moon grit his teeth until they cracked, the light of the sun began lowering ever closer to him, only the over turned train next to them shielding them. "DAMMIT!" He roared as he prepared to do something his master had forbade even the twelve moons from doing, something that even the king of demons considered to dangerous. But something that might save him.

Reaching up to his face Akaza forced his fingers into his own eye socket and grasped his right eye and with a tug he ripped it out. "Forbidden Blood Demon Art, Door of The Void!" He shouted as he clenched his fist crushing the eye in his palm, demon blood bursting out of his hand and falling to the ground below them. As the blood touched the earth it began to gather together and expand forming a large black circle around their feet, after a few seconds a dull glow began emitting from the ground.

"RENGOKU!" Tanjiro screamed again as he watched both the Hashira and the demon began to sink into the black abyss that had formed beneath them.

It was to late as only a few moments later the pair had been completely engulfed, minutes afterwards the morning sunlight would shine down on the black abyss they'd disappeared into and it would be burned away to nothingness.

Remnant

Akaza had never felt anything like this before, it was as if his entire body was being stretched to it's absolute limit. He felt no pain as he felt himself moving through the absolute darkness that even his demon eyes were unable see through, wave after wave of nausea and vertigo smashed into the entire time. How long he was in this void he didn't know, seconds felt like years yet it was over so quickly.

In an instant the darkness was burned away by moonlight and an explosion of wind slammed into the demon, the disorientation only last a few heartbeats before he managed to take in his surroundings and understand his situation. He was currently upside down several hundred feet in the air and was falling quickly. For a moment he'd actually forgotten the man who, even after clearly losing consciousness and likely being only a hairs breath from death, still held a powerful grip on his arm.

Looking down Akaza used his free arm to punch downward creating a shockwave strong enough to slow their fall slightly, turning he managed to right himself. Bending his knees he waited to hit the ground, something that only took a few seconds. He felt several bones in his legs and feet crack on impact but thanks to his demon blood they had already completely healed by the time he stood back up. Akaza took a moment to look around at the forest surrounding him, then to the man on his arm.

Akaza stared at the warrior who still held onto his arm which was impaling him. The upper third moon had fought and killed many demon slayers before, he defeated a number of other Hashira in the past. Compared to this man some were stronger, faster, more cunning and more experienced. Yet never had he faced one who had made his blood more excited than this man, Kyojuro Rengoku.

With a frown Akaza raised his free arm in preparation to deliver the final blow to this man who had earned his respect, forming a fist he brought it down towards his head. Then a tug on his shirt stopped his fist mid strike, jerking his head around to face the one who'd grabbed him. It was only for a brief moment but in the corner of his eye the demon caught a glimpse of someone. He stared at the empty space where he'd swear there had been been a girl with tears in her eyes. The forest was silent as his demon eyes scoured his surroundings for any trace that anyone was actually there, nothing.

Akaza looked back to Rengoku, he raised his fist again but as he willed himself to end him, he found himself unable to do it. This man had yet to reach his peak, he could go even further than he had during their fight. He just needed more time, just a few more years and he'd be strong enough to truly give the third moon a real battle. Finally after a few more moments Akaza lowered his his fist and lifted the unconscious Hashira up before turning to the direction he'd seen smoke rising from in the distance as they fell.

"If you can survive a bit longer you'll have earned this mercy Hashira Rengoku." He said before taking off in a full sprint.

Ansel

Jaune panted on his knees, the blunted metal training sword on the ground next to him. "Again." He said between breaths as he reached for the sword.

"No, that's enough." His father said shaking his head, the man didn't even appear to be sweating. "You aren't cut out for this Jaune, life as a huntsmen is hard and short. Give it up." His father told him as he shakily picked himself up using his sword as a crutch.

"That didn't stop you or grandpa or every other Arc." Jaune responded before lunging forward and swinging his weapon man wildly. It was to be expected that the elder Arc would effortlessly avoid each attack before raising his hand and back handing the boy to the ground. The man was a veteran huntsmen with more than twenty years of experience under his belt, he had graduated with honors from Beacon Academy. Jaune however was a fourteen year old boy who'd never been taught even the barest basics of combat.

Jaune forced himself to his knees before spitting out a glob of blood. "Aga-" He was cut off by the sound of wood cracking.

Turning his head to the forest behind their house and quickly met a pair of glowing yellow orbs staring at him. In an instant his father was in front of him holding his practice sword before him. "This is private property, you are trespassing. Show yourself now." He commanded.

After a moment the orbs began approaching, Jaune felt his heart quicken with every step closer they came. Something primal within him was screaming to run away, then the owner of those orbs stepped into the moonlight and Jaune's racing heart skipped a beat. This... person who gave off the most terrifying aura he'd ever felt stood nearly a foot shorter than his father and appeared to be completely unarmed. He had bright pink hair, pale skin that was covered in tattoo's and wore very open clothing that showed off his muscular form. Neither Jaune nor his father were really paying much attention to that any of that, instead they were staring wide eyed at the second man on his arm, literally on his arm. Blood ran down the limb that was impaling the unfortunate blonde man.

"A marechi, a shame I'm in a rush." The man spoke looking directly at Jaune.

"INDENTIFY YOURSELF NOW!" His father shouted now in a combat stance ready to attack.

The stranger looked to his father. "This man is about to die." He said raising the unconscious blond on his arm, again literally. "Take him to a healer, do this and I won't kill you." Before his father could reply the stranger raised his free hand then in a swift chopping motion brought it down on his other upper arm completely severing it in one strike. It was this sight that was finally to much for the exhausted young boy who proceeded to lose himself to the blackness of unconsciousness.

Unknown

"My strong, gentle boy." He heard the familiar voice above him as he felt fingers run through his hair.

Taking in a deep breath he was met with a familiar scent that set him at ease. "Mother." He spoke without opening his eyes.

"I'm so proud of you my son." She said as he felt her hand press against his forehead. "But you're not done yet."

Kyojuro's eyes snapped open and several things instantly made themselves known to him. First and foremost was the pain he felt across his entire body, it was a dull ache that turned to a sharp pain at the slightest movement. The worst pain was located at his abdomen. Next was that he was in a bed with several strange tubes attached to needles struck in his arms and torso that lead to multiple bags of liquid that hung from metal sticks. Then there was the repetitive beeping sounds coming from an odd looking box nearby, he wasn't sure what to make of that.

"I'm alive." He said to himself as he closed his eyes again as he thought back on what had happened. He remembered the mission on the train, young Tanjiro and his companions had managed to defeat the demon that had taken over it with his help. Then he showed up, Upper rank three demon moon, Akaza. He'd been by far the strongest demon he'd ever faced.

With great effort and pain Kyojuro lifted his hand to his stomach which was tightly bound in bandages, he winced lightly at the contact.

"Good morning Mr. Doe, how are you..." An older woman paused as she opened the door to his room holding a stack of papers clipped to a piece of wood. "You're awake! Doctor our John Doe has woken up!" She spoke in a louder voice than before.

A few moments later an old man in a white coat entered the room and walked right over to him. "Incredible, you weren't expected to regain consciousness for another week at least." The man said pulling out a small stick the shined a bright light out of one end. "Can you tell me you name young man, do you know where you are?" He asked after putting the light stick away and looking to the beeping box.

"My name... It's Kyojuro Rengoku the current Flame Hashira of the Demon Slayer Corps. I assume I'm in some kind of recovery facility." Rengoku answered clearly though based off of the confused look on the doctors face he guessed he wasn't aware of the Corps, not entirely surprising, most civilians had no idea they existed.

"The demon slayer corps, is that the name of your mercenary company?" The doctor asked.

"Yes, we were attacked while aboard a train. Were there in other casualties, how long have I been asleep?" He asked attempting to sit up only for the doctor to stop him.

"Please young man, your wounds are still healing. It's a miracle you didn't bleed out long before you were brought here, had it not been for Nicholas unlocking your aura on the way you would have died." The doctor told him as he gently push him back down into the bed. "And to answer your question, you've been here for about three weeks. I've heard nothing of any attacks on a train and you are the only patient with more than a bad cut or a fever I've treated in Ansel for many months."

Kyojuro absorbed this information with mild confusion, he distinctly remembered the train derailing. Even with no deaths such an event would be news worthy across Japan, and he'd never heard of any village by the name Ansel, certainly no cities. "How did I arrive here?" He asked.

"The captain of the towns militia, Nicholas Arc carried you. He practically kick down my door in doing so, as for how you came to be with him I'm not sure. Though he did request that I alert him as soon as you awoke, something I'm going to go do now if you'll excuse me. Should you need anything or start feeling further pain please call for Ms. Sandra here, she's been acting as your nurse for the past few weeks." The older man stood to leave.

"Before you go." Rengoku stopped the man. "I thank you both for caring for me as you have, I am forever in your debts." The smiled and nodded to him before leaving the room.

Kyojuro rested his head back on the pillow behind him as he went over several of the things the doctor had told him. No train derailment, a village he'd never heard of, the lack of any Corps presence. He knew for a fact that this Nicholas Arc person was no demon slayer, as a Hashira he was privy to information on every new member to their organization.

Closing his eyes Kyojuro cleared his mind of these thoughts, slowly he began inhaling until he reached his maximum lung capacity and held it for several seconds before releasing. Over the next few minutes he worked himself into total concentration breathing. Like all Hashira he was normally in a constant state of use of the technique, even while sleeping, but almost immediately after waking up he noticed he'd stopped. If the doctor spoke the truth, and he saw no reason to doubt him, he hadn't been breathing properly for several weeks. It likely wasn't enough to cause a weakening of his lungs but it was best to get back into the habit.

Within an hour he could already feel the effects of his breathing, his thoughts became clearer and he was better able to take stock of his bodies condition. He was surprised to say the least over the damage to his body, or more specifically, the lack there of. He could now vividly remember the battle with the Upper Rank Three Demon Moon, he remembered each wound he sustained. Most obviously was the massive hole through his torso that had doubtlessly damaged if not completely destroyed a number of his organs and completely fractured several of his ribs. He remembered taking blows to the head the had likely caused concussions, he had broken several fingers and toes in the process of blocking and dodging attacks. And of course there were the dozens of torn muscles, tendons and ligaments across his entire body that had resulted from pushing himself well beyond his limits.

Such wounds would probably put him out of commission for several months at a minimum, yet as he continued to check himself he found his current condition far less severe than it should have been. He could feel the hole in his gut had largely closed up, he could tell it still needed time to heal further but it was much further along in the healing process than it should have been. His ribs ached but he could tell they nearly completely healed, his fingers and toes barely throbbed.

"Are you awake?" A new voice made the Hashira open his eyes and turn to face the man standing in the doorway.

"I am, are you the one who brought me here?" Rengoku asked the tall stern looking blonde who, in all honesty, reminded him a bit of his of father.

"Yeah, I'm Nicholas Arc, retired First class Huntsmen and captain of the Ansel town militia. It's my responsibility to keep this town safe from whatever may threaten it, which is why I'd like to ask you a few questions." Nicholas fully entered the room and closed the door behind him. "First, who are you? The doctor mentioned you were a member of a Mercenary group named the Demon Slayers Corps."

Rengoku nodded. "Correct, my name is Kyojuro Rengoku. I was involved in an attack that resulted in the appearance of an extremely powerful enemy shortly after the derailment of our train." He explained to the older man. "I was traveling with three others, a young man with a scar over his left eye and a wooden box on his back, another boy with blonde hair and a yellow coat, and a boy usually wearing a large boar mask."

The older blonde stared at him for a short time. "Where are you right now, do you know?" He asked earning a confused look.

"The doctor mentioned this towns name was Ansel, I've never heard of such a town I admit but one can hardly be expected to know every village in Japan." Kyojuro smiled at the man.

"Japan?" Nicholas asked. "That is what exactly?"

"Our nation..." A sinking feeling began forming in his stomach.

"We're in the Kingdom of Vale son. There's been no train derailment anywhere near here in many years and there is no Nation named Japan." Nicholas walked over and took a seat on the doctors stool. "A few weeks ago I was outside working with my son when a... person appeared from the forest with you impaled on his arm. He demanded I take you to the nearest doctor before, without hesitation, chopping off his own arm. Only moments after however another limb took it's place. He tossed you to me only to completely vanished into the forest."

Kyojuro listened, a sense of dread growing with every word. "Akaza... has anyone been killed?" His voice lost it's cheer and took on a far more serious tone.

His question earned a deep frown from the older man. "None I'm aware of, I've searched the forests for any sign of him several times in the past few weeks and haven't found a trace. I'm assuming he is the powerful enemy you mentioned."

Kyojuro nodded as he pulled the blanket off of his legs. "Yes, I thought he'd been killed with the sunrise. If he's still out there-" Kyojuro forced his legs over the edge of the bed despite the incredible pain, Nicholas jumped to his feet as he did so.

"What the hell are you doing, you can't think you're ready to walk yet! You're gonna reopen your wounds!" He shouted as Rengoku attempted to stand only to immediately collapse under his own weight, all the tubes an cords connected to him being pulled out in the process. Kyojuro sat on his knees for several seconds before attempting to stand again, this time barely making it to his feet, this only lasted a moment before his legs gave out once again and he fell forward. Nicholas managed to catch him and lifted him back onto the bed. "You idiot, you wound has reopened. Doctor come here..."

All the noise around the Hashira slowly became muted as his vision drifted to darkness once more.

Elsewhere

"This place is incredible." Akaza said to himself as he looked over the city of Vale, the shining lights that as far as the eye could see. Horseless carriages moving at amazing speeds, metal boxes carrying people through the air, electricity in every building. It was beyond the demons imagination. "This is what humanity is truly capable of achieving. Simply incredible." He said sitting on the edge of the roof of the tallest tower in the the city.

It had been several weeks since he'd come to this world he now knew as Remnant, the first week he'd spent wandering the wilderness until he stumbled upon another town about a hundred miles from where he'd left the Hashira. He slew and ate a couple men that had been patrolling the outskirts of the settlement, from there he simply followed the roads at night until he came upon the massive city before him. That had been a week ago, he'd spent the last couple nights learning everything he could about this world.

Akaza was no scholar, he was a fighter yet even he found himself fascinated by all the things he'd seen. One thing in particular however had peaked his interest, Huntsmen. He'd spoken to a homeless man one evening and offered him a bottle of booze he'd stolen in exchange for some answers about the world around him. Huntsmen the man told him were warriors who harnessed the power of their very souls to fight the creatures of grimm. He hadn't yet encountered one but the very idea of facing one was enough to excite the demons blood.

The creatures of grimm were of mild interest to the upper moon, he'd come across several along the roads. They hadn't paid him any mind what so ever as he passed them by, one of the smaller wolf like ones had approached close enough to smell him only to lose interest moments later and run off. He ambushed a couple of the larger bear types out of curiosity and was left disappointed by how weak they were, one kick had been enough to completely tear one in half. They were similar to low level demons in terms of raw power but lacked the near immortality and intelligence, though they weren't vulnerable to sunlight leaving the upper moon confused over what to think of them.

Standing from the edge Akaza jumped from the tower, the air blasting through his hair was a pleasant feeling though it only lasted around ten seconds before he righted himself and slammed down onto the concrete alleyway creating two large foot deep holes where he'd touched down. Pulling his feet free from the ground he walked passed the pair of homeless who'd been sleeping bye a trash can nearby that were now wide awake and staring at him.

Stepping out onto the street Akaza began walking along the side walk without any actual direction, something he'd found himself doing quite a bit these past few weeks. The Door of the Void was a forbidden technique for a reason, it was a complete shot in the dark as to where you'd end up. Lord Muzan had gathered he and the other twelve moons at the time around a hundred years ago and had explained it to them in detail. The technique essentially ripped a hole in reality for a very brief time, according to the king of demons this hole lead to an infinite number of worlds and planes of existence with infinite possibilities. Akaza hadn't completely understood the explanation, again he was no scholar, but he was able to piece together the basics of it. If he were to use it again the chances of him returning home were all but nonexistent, he'd have no way of even guessing what kind of world he'd wind up in next time.

This left him with a major problem, he had no purpose. For as long as he could remember Lord Muzan had given him direction, now he was separated from his lord. "AAAAAAAAH!" He suddenly shouted startling everyone around him. "What the hell do I do?!"

Two Weeks Later

"Slowly now, don't push yourself to hard." The nurse coached Kyojuro as he walked between a pair of parallel bars.

Kyojuro Rengoku was currently thanking whatever gods existed in this new world called Remnant he found himself in that his fellow Hashira weren't here to see him in this humiliating state. It had taken several weeks of further rest and healing before he was able to stand once again, he'd then attempted to take a step only to collapse to the floor. It was an incredible odd and infuriating thing to have lost the ability to walk, something he'd been doing since before he could even talk. It wasn't uncommon for someone greatly injured to have to relearn to perform simple tasks such as walking and standing but he was a Hashira dammit! He'd fought and killed a number of Demon moons in his career as a Demon Slayer, he was a master of the flame breathing style, learning to walk again shouldn't be this hard.

"And stop, take break." The nurse told him once he reached the end of the bars.

"I can continue." Rengoku said turning to do it again.

"No, your legs are trembling, you need to rest." She responded walking over to the wall and grabbing his wheelchair. "I understand that it's frustrating Kyojuro, but we've only been doing this rehab for three days now and you're already walking very well. After an injury like the one you had it should take months to get where you are now, you should be proud." She told him as she slowly helped lower him into the chair. "At the rate your improving it should only be a few more weeks before your back on your feet. Now come on, a little sunshine will be good for you."

Kyojuro sighed as he leaned back in the chair and allowed the woman to wheel him outside and onto the front patio of the clinic, closing his eyes he focused on his breathing once more. He'd managed to ease his body back into total concentration breathing nonstop, it was am extremely taxing technique to those without the proper conditioning. As a Hashira he'd put his entire body through hell for years so it could withstand the stress the breathing caused, when weighed against the advantages however it was wasn't even a question whether or not it was worth it. He was stronger, faster, had greater mental capabilities, his stamina was second to none and he even healed faster.

Opening his eyes once more he looked up to the sky. "Even with all of that, I still lost." Looking down at himself he frown at his now skinnier and less defined form. That demon, Akaza was out there in this new world, a world with no knowledge of demons. The havoc he could cause was limitless, and he was likely only growing stronger as he killed and devoured completely without opposition. "Dammit!" He shouted bringing his fist down on his leg.

He felt so useless in this chair unable to even walk, then a face came to mind. A young man completely surround by Hashira who was being forced to watch as his younger sister was tortured, a girl whose only crime was being turned to a demon against her will. Even as he was held down by another Hashira he fought until his bones were at their breaking point so he could save his sister, even knowing he'd never reach her. Despite all of this he never once gave into despair.

A small laugh escaped his lips. "Tanjiro, I truly am unworthy of the title of Flame Hashira to allow your soul to burn so much brighter than my own." A smile grew across his face once more.

One Week Later

"Eighteen, nineteen and twenty." Kyojuro counted as he performed squats, a very basic exercise but it was the limit of what his body could currently handle. Taking a deep breath Kyojuro stood up straight and walked over to the dresser in his hospital room and grabbed a towel off of it and wiped sweat from his face. Turning to the device he'd been told was a clock he noted it was only four in the afternoon, still a while before dinner would be served.

Reaching for he crutch he decided a walk might be a nice way to kill time. Slowly exiting the clinic Kyojuro began making his way down the dirt path that lead into the small town of Ansel. The sounds of nature were pleasant to the hashira as he walked. The clinic was located to the northern wall of the town, the wall themselves were mostly wooden with areas reinforced with steel. The walls didn't surround the entirety of the town however, the eastern half of the town was protected by a lake and the southern side had a thick forest with a fast moving river that ran through it.

Kyojuro continued his walk for a another hour until he arrived upon the edge to the forest, according to Nicholas Arc the upper third moon had emerged from these woods with him still impaled on his arm. Raising his hand to his chest Rengoku sucked in a deep breath and held it for several seconds before letting it out, a wide smile spreading across his face. "Next time will be different." He said to himself as he turned to leave only to pause at the sound of wood hitting wood.

Out of curiosity he began walking towards the source and soon found a blonde young man practicing with a wooden sword on a tree. With the briefest glance Kyojuro could tell the boy was a complete novice with a sword, everything from his stance to his grip were way off. Even still he could tell by the bruises on his body and the blisters on his hands that the boy practiced hard.

"Bend your knees and move you hand further up on the grip." He called out making himself known.

So as many of you have likely noticed I've taken a large portion of 2021 off of writing for personal reasons. It's my goal to get back into the writing groove I use to be in. I'm forever grateful to everyone who've stuck it out this long with me. Leave me a review and tell me what you all think. LATER.