(Happy birthday to me)
~~~~
The world is a blank canvas, created by the gods above. Upon it, we humans painted with the colours of our lives—our joys, our sorrows, our fleeting moments of peace.
Somewhere, a mother hummed a lullaby as she tucked her children into bed. A newlywed couple lay together, wrapped in the warmth of their first night. An old man laughed and drank with his lifelong friend beneath the moonlight. It was a night of tenderness and celebration, and for a moment, the canvas glowed with gentle, radiant hues.
But in this world full of peace, there was violence, and in this world full of brightness, there were dark stains.
Demons.
The mother singing lullabies to her children was nothing more than a gory mess by the next morning. The wife who should have been in the warm embrace of her husband now wept under the icy touch of his remains, and the old man and his buddy were never seen again.
"God is the one who provided the canvas, we humans brought our colours to paint it, and Muzan Kibutsuji brought his own filth to desecrate it."
"Demons are a black stain in the world, and we, Demon Slayers," I muttered as I slowly unsheathed my sword, "are the bleach that removes the stain."
~~~~~~~
What a pleasant night. The moon hung high, casting silver light over the land. Trees rustled softly in the breeze, and ignorant humans slept peacefully in their homes.
A perfect night for hunting demons.
"Of course that will never happen to me," Demon Grunt 1 said, sitting on top of a tree. "The Demon Slayer Corps probably doesn't know I even exist."
Demon Gru- fuck that's a long name for someone unimportant. I'm just calling him DG for now.
Anyways, DG was a weak coward.
That's right.
This demon was born 4 months ago, yet it has only consumed 8 people, averaging a whopping rate of 2 humans per month. A statistic so low, even human cannibals can easily surpass it.
''Of course I'd eat sparingly,' The demon hissed. 'If I eat too many people from the same village, they'll report the disappearances, and then the Demon Slayer Corps will send a Slayer, and that would be the end of me. Besides, do you know how hard it is to find two villages far apart from each other?'
Just use Google Maps, are you stupid?
Regardless.
It was a cautious demon, perhaps too cautious, considering it had barely eaten people. Still, in the end, this "weak" demon was alive and feasting on humans, and those "strong" demons were eternally burning in hell. So who's the real winner here?
Feeling giddy, DG climbed up on top of the tree and laid his eyes upon his kingdom (He has never been here), declaring himself as king of this mountain.
Sure, climbing up a tree on the highest peak mountain was risky, where you're effectively visible to everyone in a huge radius, but what are the chances of that happening?
"DEMON! DEMON! CAW"
DG's heart nearly stopped as soon as he heard that shout.
'Seriously? What are the chances… It's like god hates me.
Well, he is a demon.
"Fuck, a Kasugai crow" DG hissed looking upwards "I got overconfident"
*Zwim*
A sharp buzzing noise cut through the air as his eye shifted—from a dull, human-like black to a piercing reptilian green. In an instant, the cloak of darkness surrounding the night was unveiled, along with his Visual Acuity nearly doubling in range.
(Visual Acuity- The maximum range of vision of the human eye)
"If it's someone strong, I'll run. But if it's some weak…" DG snickered, trying to mask the tremble in his voice. Slowly, he stood and scanned the forest below, his eyes darting, searching for the Demon Slayer that the crow had warned.
"Please be a weak one. Please be a wea—"
Shudder.
A chill rippled through his body. Every hair stood on end. His throat, despite being a demon, felt dry as sand. Something was wrong. Very wrong.
Instinct took over, and his eyes locked onto the source of his unease.
"Wh-" DG murmured in disbelief as he rubbed his eyes as if he could not believe what was happening. "He-he's-HE'S FLYING?"
That's right.
The Demon Slayer was flying in the air while doing some cool ass backflips.
"Not weak," DG screamed in fear, "THAT'S NOT A WEAK SLAYE-"
"Martial Union Water Breathing Eighth Form: Waterfall Basin"
Unfortunately for the demon, the slayer was approaching him faster than the speed of sound. Even being in a trance for just a second was more than enough time for Aoyama to come crashing down on his head.
*squelch*
First, there was a wet, ugly crunch. My leg pierced his skull, ripping clean through brain, chest, abdomen… and finally, his balls, completely cleaving him in half.
A one-second fatal gay footjob. A quickie if you must.
Then came the crack of impact against the tree beneath him. My leg continued its descent, splitting bark and trunk with ease, cleaving the tree clean in two.
The explosion followed—wood bursting into hundreds of splinters, each flying out like shrapnel, carrying the force of tiny missiles.
Then, my leg hit the ground.
*BOOM*
And everything exploded.
As if hit by a third nuclear bomb (or the first one, considering WW2 hasn't ended yet), a sound akin to a hundred exploding dynamites rang out. The ground beneath me completely caved in, as if it were made of cotton rather than stone.
A massive cloud of dust surged into the air from the impact, swallowing the forest in a thick, choking haze. For a few moments, everything was silent—buried in grey.
Then, the dust began to settle, and I could finally see the aftermath.
"Holy shit"
'Atleast what was left of it.
It looked like a meteor had just hit this place. The crater from my impact was atleast 6 meters deep (18 feet) and the area of impact was atleast 4 meters. The trees around me had been completely uprooted by the raging winds, along with any other lifeform unfortunate enough to have been here.
"Except you"
Except the demon in front of me. His body, scattered in dozens of pieces, slowly wriggled around and regenerated.
'Fascinating,' I thought, looking at the demon regenerate from what was effectively a missile strike. 'Even a lower-ranked demon can survive an impact like this as long as there is no sunlight involved.'
*Flop*
As soon as I finished reviewing my thoughts, the pieces stopped wriggling and fell apart. In a matter of seconds, the scattered flesh slowly disintegrated into ashes as if the world itself intended to mock me.
'... Never mind' I sighed, though it was logical. If a weak demon could survive a missile blast, that would have been truly absurd. 'I'm probably the first person to kill a Demon without using anything related to sunlight.'
Though it was just a thought, the statement was absurd. No one in that world was able to outright kill a demon without the help of the sun, with the exception of the Demon King, who could kill demons by controlling their cells.
Unfortunately, there's no way this would work on an Upper Moon; those guys have insane regeneration. Besides, they're not going to sit still while I unleash that attack.
'But, I'm satisfied for now,' I thought, clenching my fist. 'Because now I know how strong my body is'
The reason why I wanted to fight a demon was for one reason: to measure myself in raw power compared to a demon.
The effect of Martial Union:Stone Breathing was to enhance the body to an extreme degree, eliminating most imperfections and empowering all the muscles and bones while still maintaining a perfect composition, meaning that I now have three techniques actively enhancing my physical state.
Martial Arts + Repetitive Action + Stone Breathing.
I wished to test the effectiveness of this combo by having a straight-up brawl with a demon to see if I could surpass its base physical stats.
'And it's worked splendidly,' I thought while raising my arm.
Specifically, one full of splinters.
And it wasn't just the arm. When the tree exploded into splinters, it pierced every part of my body, yet they could only slightly embed themselves in the skin, as if the skin were too tough to go through.
And if the skin is so tough, you can only imagine how tough the muscles and bones are.
'Even my skin's much tougher now,' I thought while shaking the splinters off. 'My body…It should have surpassed Gyomei's by now.'
*twitch*
'Who?'
Instinctively, my body went into combat mode as my ears twitched from the sound of footsteps approaching.
'That distance…' I frowned as if trying to calculate the distance 'About 50 meters?'
Repetitive action is a technique that not only works by strengthening the body like Total Concentration, but it even enhances the five senses of the body to an absurd degree. Currently, Aoyama, who has just learned this technique, can hear sounds from about 80 meters, and Gyomei, who is a master of it, can likely hear sounds from a much farther distance.
'Heavy footsteps and from the distribution of vibrations into the ground, then the area of the foot, likely a size 9, and the height from where the whistling of sound ends…I'd wager about 5 feet 10 inches, meaning the one approaching is most likely a male,' I thought while frowning, 'and the clinking of metal…sounds a lot like a sword.'
'The speed is beyond a human's, about 256 km/h, and the clanking of swords,' I thought while relaxing. 'It's a high-ranking Demon Slayer, and that pattern of breathing…Flame?'
…
"There's no way it's Kyojuro, right?"
"HAHAHA"
"It's Kyojuro."
Kyojuro Rengoku, the Flame Hashira. He was born into the Rengoku family, who were practitioners of Flame Breathing. Before him, his father Shinjuro Rengoku was the Flame Hashira.
Unfortunately, after his wife's death, Shinjuro discovered the records of Sun Breathing. After reading them and being affected by his wife's death, Shinjuro completely stopped being a Demon Slayer, instead indulging himself in alcohol daily. When asked why, Shinjuro just said that no matter how talented or determined a person was, they would never reach the level of a user of the Sun Breathing.
Of course, any Hashira who climbed to their position through sweat and tears would atleast be a little discouraged when they realize a 8 year old Yoriichi had not only easily reached their strength, but even mastered other techniques like STW or the Mark, and later on grew older and became powerful enough to defeat the Demon King in a 1v1, despite having never trained once.
However, that discouragement would only last a while. After that, some Hashira would either take it as encouragement and start training to their fullest in hopes of reaching that strength, some Hashira would remain indifferent, and some would completely break down in disbelief.
I'm getting off topic…
After Shinjuro Rengoku unofficially stepped down, the Demon Slayer Corps was in desperate need of a new Flame Hashira. Kyojuro Rengoku was then given the mission of slaying a Lower Moon Demon that had appeared, and if he succeeded, he would become the new Hashira.
(To become a Hashira, you must reach the Kinoe rank and slay 50 demons. You can also kill one of the 12 moons regardless of rank, and be promoted to one. Additionally, only one Hashira for a certain breathing style can exist at one time. You cannot have two Hashira who practice Water Breathing or any other breathing.)
Rengoku Kyojuro then later died while fighting Upper Moon 3, a few years later during the Mugen Train Saga. Rengoku's younger brother was completely talentless in Flame Breathing and had no desire to become a Demon Slayer, meaning the Rengoku family essentially ended after Kyojuro's death. Of course, that didn't matter in the end because the Demon King was killed soon after, and all demons in the world vanished after his death.
There is no need for Breathing Techniques in a peaceful world after all.
"Greetings! My name is Kyojuro Rengoku. May I know your name, fellow Slayer?"
Unfortunately, the Kyojuro in front of me was not the one who almost killed Upper Moon 3, but the one who hadn't even fought a Lower Moon yet.
'Still,' I thought as I looked at the laughing figure, 'He's pretty strong.'
Unlike Gyomei, who was lucky enough to be born with a strong body, or I, who artificially got one through techniques, Rengoku's body was a result of selective breeding over a course of centuries.
"Slayer! Are you here?"
Not something like arranged marriage, just more of a byproduct of coming from a family of multiple Hashira..
"Hmhm, in that case, Greetings Slayer, my name is Kyojuro Rengoku, a practitioner of Flame Breathing, may I have your name?"
Muscles and bones that were so perfectly selected from the other dozens of genes that they almost shone, a figure just perfectly bulky and tall enough to properly wield a Nichrin blade, as if his entire existence centered around one.
'It's like his body was modeled by the sword itself'
*thwip*
Without thinking, my hands swept upwards, just stopping Rengoku's hands from touching my shoulder.
"What speed!" Rengoku smiled as he withdrew his hand. "I believed you were lost in thought."
"I would be a terrible slayer if I could get lost in thought," I murmured, "Aoyama Yuito Daichi, Water Breathing."
"Aoyama Yuito Daich?" Rengoku said in thought, before smiling widely, "Ah, the Tsugoku of the Stone Hashira who requested an audience with my father to teach you Flame Breathing!"
"Tsugoku? So that old man has officially accepted me?"
"Indeed! To become the disciple of the strongest Hashira of this generation, I wonder how strong you are. Also, please refrain from calling your teacher 'Old man', teachers should be treated with respect."
"I will keep that in mind."
"Then," Rengoku began again, though with a slightly less excited voice, "I must ask…are you the reason for this crater?"
…
Fuck
~~~~~~~~
"UMAI"
*thud*
'My money…the second most important thing after my life…my money…'
Gazing at the 25 stacked bento, I let out a quiet prayer for my empty wallet. It didn't help that officially I'm still a Mizunoto, which means I get a terrible salary, and now I'm being forced to spend my savings on this gluttonous bastard
"UMAI! Let this be a lesson!" Rengoku shouted mid-bite, forcing me to dodge grains of flying rice, "That you must always be mindful of the nature around you! You could have collapsed the entire mountain, which would—UMAI—have been devastating!"
"…You're overestimating this world."
Demon-Slayer was a pretty low-level world. No being in this world could actually destroy a mountain.
'Haah, I can't spend all my time on this world, I'm gonna have to try going to a world that's actually decent soon' I thought as I mindlessly tapped my fingers on the counter 'Once I get Sun Breathing and the Demon Slayer Mark, I'm becoming a Demon and dipping out of here'
Yeah, that was my original plan.
The entire reason why I came to Demon Slayer in the first place was to learn every single ability in this world, including Blood Demon Arts.
'After all, even though this world is weak, it has useful abilities, ' I thought, mentally counting ' X-ray vision, Physical enhancement, minor control over sunlight for humans, and mystic abilities, regeneration, and near-immortality for demons'
You can't deny those are some pretty sweet abilities, right?
'I don't have to worry about the sun either when I master sun breathing. And if that fails, I could just get the Blue Spider Lily. I know where it grows after all.'
My gaze drifted to Rengoku, who sat across from me, happily slurping down some cheap ramen like it was the finest cuisine in the world. Completely content. Completely unaware.
'But…It's changed now'
The real reason I even started hopping between worlds—the reason I came here at all—was to find a way to heal the friends I left behind. My friends in 1A. The ones who got hurt because of me. If I hadn't intervened, they would've walked away with a few bruises at most. But no—I had to make it worse.
'Not the time for self-depreciation'
Right,
Anyway, the plan was simple. I'd turn myself into a perfect demon, go back, temporarily convert Class 1-A into perfect demons too—just long enough for them to heal—and then disappear. No more world-hopping, no more drama. Just sit in my classroom, keep my head down, and invent cool shit until I die of boredom or old age, which I wouldn't because I would be a demon.
'I mean, I come from a peaceful world, I don't want to risk my life doing this shit' I grumbled in my head 'I'm neither brave nor determined enough to do something like this. I'm just a middle-schooler, for god's sake. Not a Shounen Protagonist'
I sighed, feeling the weight of the world crush me. Forget that, let's just continue my third-rate plan for now.
'I mean, if I'm turning them into demons, I might as well turn All-Might into one so he could heal his abdomen' I thought 'After all, if demons can survive getting cut into tiny pieces, and even regenerate their whole body as long as only a limb remains, surely an abdomen wound would be no problem'
I mean, isn't that literally perfect? All Might's back in his prime, Izuku is a demon, so he doesn't need to worry about OFA's backlash, and with his regeneration, he could easily master OFA in a matter of a month or two.
A demon's regeneration far surpasses that of AFO's after all, especially the regeneration of an Upper Moon.
And if they train hard enough, they could even unlock a Blood Demon Art. There's no way Shigaraki would win against an Izuku who has 100% control over OFA, immortality, regeneration that surpasses even AFO's, and a Blood Demon Art.
I mean, hell—Izuku didn't even fully unleash 100% OFA by the end of the manga and still won. Sure, it was a kind of crappy ending, but he won. This time? He wouldn't just win—he'd crush Shigaraki. And finally fulfill his dream of becoming the Number One Hero.
And the best thing, BDAs are Quirks, so even if Izuku loses his Quirk, he can still be a hero.
So, simple plan: heal everyone, expose Aoyama—not me, the blonde twink Aoyama—as the traitor, or just kill him outright if it's more convenient. Heal All Might, sit back, and let the Heroes win. And since I'd be one of the key people who made that happen? Boom—instant fame, a comfy life, and recognition as a genius inventor.
And if that doesn't work out? I'll just become a Hero myself. Honestly, I'm already more than strong enough to rank in the Top 10.
'Atleast that was the plan at first'
My thoughts drifted back to everyone I had encountered. Urokodaki, Tanjiro, Gyomei, Kenzo, and even that group of misfits I met in the Final Selection.
'What about them?' I thought grimly, 'They're close to me as well aren't they?'
Even if I become a demon and score a perfect ending for the MHA world… what about this one? Am I just supposed to betray everyone here? Sprout fangs and regeneration, turn into something they've sworn their lives to destroy, and then vanish like it meant nothing? Just run back to U.A. and pretend none of it happened?
'If I did that, I wouldn't be able to sleep from the guilt'
"This is so complicated."
"Hm! What is troubling you, my dear friend?"
"Friend?" I muttered, shaking my head, "It's a personal issue, you don't need to worry."
Right, the first thing I need to do right now is learn Flame Breathing.
"Rengoku-San, I heard your…" I said, pausing for a bit, unsure of how to phrase the question, "Your father is…going through something?"
Great going Aoyama
"Umu," Rengoku nodded, surprisingly unbothered. "The Flame of Passion within Father has indeed dwindled. But worry not. Even if he refuses to teach you Flame Breathing, I shall take up the role in his stead! Though…" he added with a sheepish grin, "my instruction may not compare to that of a Hashira."
"Whew," I sighed as if a weight had lifted off my shoulders. "Thanks, Rengoku-San."
"It is all well," he said with that ever-burning smile. "Though there is no need to call me by my surname. I believe we are well-acquainted enough to address each other by our first names."With a satisfied grunt, he finally set down the bowl of ramen, the mountain of food seemingly no match for his appetite.
"Aoyama," he continued, voice full of warmth, "you may call me Kyojuro."
"I suppose it would be awkward to call you 'Rengoku' when both you and your father share the same last name," I said. "Then… Kyojuro it is."
"Very well," Rengoku nodded, though a subtle shadow crossed his face. "I do not wish to give you false hope, so I will say this plainly. Father will most likely not accept you. After Mother's death, he shut himself in his room and rarely comes out."
"Really?" I replied, feigning surprise, even though I already knew.
"Not just that," he continued, his voice quieter now, "he's refused to take on any more students. He even disrespects our family's legacy as Flame Hashira, scorning the art of Flame Breathing itself after reading about something called 'Sun Breathing' in our ancestors' notes."
"Is that so…"
I continued off in thought.
'Sun Breathing is definitely strong, yes,' I thought, 'But it's not godly.'
To be clear, Yoriichi wasn't strong because of Sun Breathing; he was just built differently. The technique helped him, but it didn't make him.
Sure, Sun Breathing is objectively stronger than the derivative forms, but it doesn't elevate the user to some divine plane. Take Tanjiro, for instance. Even at the very end of the manga, after mastering Sun Breathing, he couldn't take down a heavily injured, drugged Muzan without help from the remaining Hashira. That alone proves it—it's powerful, but it's not a miracle.
It's like Wood Style in the Naruto world. Everyone hypes it up like it's inherently legendary,but it was only considered mythical because Hashirama used it. When someone like Yamato tried, it was… fine. Functional. Nothing world-shaking. The technique itself wasn't special—the user was. Hashirama was the reincarnation of the Sage of Six Paths' son. Of course, anything he touched would look divine. Wood Style was just a medium; his overwhelming chakra, battle intuition, and monstrous healing factor were what made it terrifying. The same principle applies here. Sun Breathing only looks godly because Yoriichi was a goddamn anomaly.
'But how do I make Shinjuro understand that?'
Yes, I wanted to help Kyojuro's father out of his depression. It was only because I wanted to learn Flame Breathing and not because Kyojuro is my friend now. It was purely tactical. I needed Flame Breathing, that's all.
'Wait,' I thought,t my eyes widening. 'What if I…'
"Kasai"
"CAW"
"Hm?" Rengoku hummed in confusion. "What are you doing, Aoyama?"
"Send a message to Urokodaki-Sensei" I whispered as I bent down to Kasai's leve ignoring Rengoku's words for nowl "To send Tanjiro to the Flame Hashira's mansion"
"CAW! MESSAGE RECEIVED! CAW"
'That's right' I thought while watching Kasai fly off 'I don't need to explain anything to him, I just need to show him.'
Thanks to what I told Urokodaki-Sensei before I left, Tanjiro never learned to use Water Breathing; instead, he trained in his Honokami Kagura technique this whole time.
While this Tanjiro would undoubtedly be much stronger than his canon counterpart, he has only been training for a few months. There's no way he would be stronger than a veteran slayer and a Hashira candidate like Kyojuro or a literal Hashira like Shinjuro.
So, all I need to do is have Tanjiro fight either of them and lose.
'Sorry, Tanjiro, you're gonna have to get a bit beaten up for now.'
"Don't worry, Kyojuro, you're going to love this."
"I see?"
"Then," I said, turning around in excitement, "Shall we go now?"
"HAHA," Rengoku laughed. "Your excitement is palpable, just like a little kid's."
"Well," I nodded, "I am only 15."
Rengoku's laugh stopped upon hearing that.
"...You are 15?"
"Yep"
"Hm." He folded his arms, expression shifting into something more contemplative. "That is quite young. I must admit, it is a bit demoralizing to be bested by someone who is my junior by three whole years."
"BUT—" Rengoku suddenly bellowed, nearly making me jump out of my skin. Uwaa?!
"THIS ONLY MOTIVATES ME TO TRAIN HARDER! HAHAHAHAHA!"
His voice echoed through the trees like a thunderclap, his laughter loud and fiery as ever. I swear, even the birds took off in a panic.
'Right,' I thought as I smiled grimly, 'This is the difference between us.'
Despite having been onscreen for only about an hour, he had captured the hearts of many fans because of his charisma and motivation.
'Compared to that, I can only be the dark vacuum of space'
Silent. Heavy. Unmoving. The kind of person who observes, calculates, and manipulates from the sidelines—always thinking too far ahead, never letting the moment carry me away.
'But, that's fine,' I thought with resolve, 'If I can't be the sun, then I'll be the infinite space that holds everything together
And for that
I need to become stronger.'
~~~~~
"Flame Breathing second form: Rising Scorching Sun"
*woosh*
A gust of wind kicked up as the bearer of the blade unleashed her technique. The moment her sword cut through the air, a wave of heat followed, and a faint breeze rippled through the clearing.
Unfortunately, swinging a sword requires a lot more than strength.
"Uwaaa, I can't do it"
Even though the force of the swing was impressive, if one looked closely, the quantity of flame produced from the swing was minimal, like the minimal quantity of water produced by someone like Murata when he used Water Breathing.
"Everyone tells me that I'm supposed to swing with my whole body instead of my arm," She muttered, pouting. "But what is that supposed to mean?"
[Mitsuri Kanroji
Rank- Mizunoto]
(Official info from Rengoku Gaiden)
And then, as if reality shifted, Mitsuri's arms turned from normal human arms to chibi arms.
"I mean," Mitsuri pouted, flailing her dumpling-like arms, "This isn't a manga where I can suddenly understand something in the middle of a battle, can I?"
*slide*
The sliding of doors interrupts the pink gremlin's rant.
"Um," A meek voice came from beyond THe door. "I brought some snacks."
"WAAH SENJURO," Mitsuri cried, tackling him
"W-wait, the snacks, THE SNA-"
A peaceful atmosphere settled over the estate. One might assume that the bond forming between them—akin to that of an older sister and younger brother—meant tranquility throughout the grounds.
Unfortunately, while one room echoed with cheer and warmth…
Thud
…another was steeped in silence and gloom.
"Tch."
Shinjuro Rengoku clicked his tongue in annoyance, setting his sake gourd down with a dull thud. His eyes remained fixed on the letter in his hand, brows furrowed in distaste. Slowly, his expression twisted into one of bitter disgust.
"That old fool… he's still alive?"
[Shinjuro Rengoku
Rank: Hashira]
*RIIPP*
Without hesitation, Shinjuro tore the paper into tiny pieces, curmpling them into one ball and throwing it outside his room.
"Another fool wants to learn Flame Breathing," Shinjuro grumbled, lying down on his futon. "Why don't the Slayer Corps understand that resources are better spent trying to revive the art of Sun Breathing?"
…
"Wait"
Shinjuro's eyes widened, immediately getting up as a thought struck him.
'The student of the former Water Hashira, and the Tsugoku of the Stone Hashira, yet he still wants to learn Flame Breathing.
Is he…'
As the thought struck him, Shinjuro's indifferent eyes surged with the tiniest bit of anger.