Chapter Text
The first time he meets his Sensei, it’s raining.
Genya is a few months shy of thirteen and just a little bit terrified. Sanemi had been gone for just a few years when Genya had overheard a conversation between two men passing through town. Those men, it turned out, were a pair of Tsuchinoto who had just gotten word about the appointment of a new Wind Pillar to the Demon Slayer Corps; a violent, foul mouthed young man with snowy hair and scars decorating his face. Genya had immediately sought out the Corps and tried to find a trainer of his own, but it had quickly become apparent that he couldn’t perform even the basics of a breathing technique, let alone master one. In his desperate frustration he’d resorted to something all together rash (he can still feel the resistance of raw, flexing muscle under his teeth, taste the salt and metal of blood on his tongue) and ended up at the Butterfly Estate waiting for, what he thought, would be his sentencing.
Which is why he’s so surprised when the Flower Pillar’s younger sister, Shinobu, comes to fetch him.
She’s silent as she leads him through the quiet halls of the Estate, but he can almost feel the disapproval radiating off her.
It’s as they approach the front door that voices reach them. Turning the corner, they can see Kanae speaking with someone who’s just come through the door. Water drips from the wide brimmed hat, darkening the shoulders of the coat they're wearing, falling to the floor even as they reach up to pull the hat away.
“How was your trip, Reimei-san?” Kanae asks, accepting the hat from the woman standing in her foyer.
“Well enough, thank you, Kanae-san.” The woman, Reimei, responds, but Genya doesn’t hear any other part of their conversation because he is completely transfixed.
Reimei is a little taller than Kanae, putting her about half a head taller than him. She’s only a few years older than him, too, probably around the same age as his brother, but the lithe, easy grace with which she moves speaks of an accomplished, seasoned warrior.
But what fascinates him the most is the fact that her hair is a bright, vivid red, like the petals of a camellia. Pulled into a bun at the nape of her neck and partially covered with a kerchief, it’s still eye catching enough to be the first thing he notices. The second are her eyes, grass green and suddenly fixed on him curiously.
“Are you Genya-kun?” She asks, stepping up onto the hardwood floors now that she’s shed her muddy shoes and wet coat, revealing a standard Corps uniform covered by a green and white yagasuri patterned haori. He nods dumbly, staring up at her in awe. He’s never seen such coloring on a person before and he’s embarrassed at his own fascination. She smiles at him, gentle and warm, before offering him a small bow.
“My name is Reimei. I hope we get along.”
He soon finds out that Reimei is a Kinoe ranked member of the Corps, second in strength only to the Pillars, and his newly assigned Sensei. He’s surprised, so sure had he been that no one was going to take on someone who would eat demons to assume some of their traits. Learning that Ubuyashiki-sama had specifically assigned Reimei to him had confused him even more, but that confusion had turned to understanding in less than a week.
They leave the Butterfly Estate the day after Reimei arrives, heading towards Kyoto at a leisurely enough pace. Reimei doesn’t seem to be in any particular hurry, stopping every now and then to show him a new technique he can try. Most of them are simple kata and physical exercises to increase his stamina, and he practices them whenever they stop.
Four days later sees them on the outskirts of Kyoto, dropping off their scant belongings at a rather nondescript looking inn. Until, that is, Reimei quietly points out the family crest hanging by the front door, surrounded by Wisteria flowers.
After that they start their patrol, Genya trailing after Reimei through the heart of the city, slightly uncertain but determined even as the afternoon darkens into evening. They wander for some time, watching the population of the city flow through the streets like a river. They don't stop again until close to midnight when his stomach makes itself known, growling loudly in the quiet.
Reimei tilts her head, gentle smile never wavering even as Genya ducks his head, utterly mortified.
“How does udon sound?” She asks him, startling him out of his embarrassment.
“Y-yes please, Sensei.” He mumbles under his breath.
They head back towards the more residential part of the city, settling on a little stall just off of one of the main boulevards. Reimei orders two bowls for him with extra tempura and one with an egg for herself.
“As my student, it's my responsibility to take care of you. And growing boys need more food.” She explains at his confused expression.
“But Sensei, you’re only a few years older than me.” He points out and she laughs, the sound bright and clear in the quiet night.
“Maybe, but I’m not really expecting to get any taller. Dig in.”
It’s as he’s starting on his second bowl that he feels Reimei go completely still at his side.
“Sensei?” His voice is only slightly muffled by the food he's actively shoveling into his mouth, but she isn’t looking at him, instead staring off into the darkness unblinkingly, eyes eerily bright.
“Please stay here, Genya-kun. I’ll be gone no longer than an hour. Stay in the light.” She says, setting her bowl aside and standing smoothly from her seat.
“But...Reimei-san?!” But she’s already gone, disappeared like just another shadow into the dark, leaving Genya stunned speechless.
Glancing to the side he can see that she’s barely touched her own bowl, having only picked lightly at the noodles.
One minute turns into ten, then twenty, and Genya’s worry only mounts. Finally, with a fearful gulp, he grips the training blade he’d been given when he first started trying to learn breathing techniques and sets out into the night.
He doesn’t have anything to go on, only his poor senses that only marginally improve when he tries to dreg up the last scraps of the first demon he’d eaten. Even with slightly better than average night vision he still stumbles through seemingly abandoned streets for a solid fifteen minutes before he hears it.
It starts as a low growling, the reverberation picking up strength as he follows the sound until he can feel the thump of it in his throat. It nearly makes his eyes water, but he doesn’t stop, his worry for his new Sensei only increasing.
He’s just turned into another empty street when the growling suddenly changes into a horrible, ear splitting shriek that splits through both the night and his eardrums loud enough to make him wince. He stumbles, fear making him shake, but he forces himself to breaks into a run, reaching the next corner as the shriek is petering out, turning to a pitiful whimpering before falling silent entirely just as he rounds the bend.
Genya skids to a stop and freezes, his breath feeling like a lead weight in his chest as the sight before him comes into focus.
Halfway down the alley a streetlight illuminates a slumped figure, limbs akimbo where they'd collapsed against the nearest wall, not quite glassy eyes scrunched in agony. The body shudders, jerking unnaturally each time the person crouched over them rips deeper into their insides. A terrible crunching reaches Genya’s ears, the sound of bones being snapped like toothpicks under uncaring hands as layers of skin and fat and flesh are peeled back, revealing the still beating heart. The body twitches only once as the organ is ripped free, finally starting to crumble as teeth set into tender muscle.
It only takes a few moments for the heart to be consumed, but to Genya it feels like an eternity because all he can see is red.
The red of blood staining the pavement.
The red of sharpened, dripping claws.
The red of the harvest moon hung heavy and fat in the sky above them.
The red of his Sensei’s hair and eyes as she straightens from her crouch, wiping at her mouth with the back of a hand, smearing blood across her lips and chin. The crimson of her sclera makes the green of her irises even brighter, more unnatural, sharper as they cut to him. The sound of her footsteps is oddly loud, echoing in his ears as she approaches.
Genya has no idea when his legs collapsed out from underneath him, but he only fully realizes it when Reimei has stopped in front of him, that much taller from his position on the ground.
“I told you to wait at the stall.” She says, voice a little deeper, a little bit warped. Genya tries to swallow around his paper dry throat, because knowing he’s done this, eaten a demon, is nothing like seeing it happen before his eyes.
He manages to turn away from her at the last second as he feels the burn at the back of his throat, heaving violently between great gasping breaths that do nothing to reduce the panic quickly rising in his chest. He nearly jumps when a cool, dry hand touches the back of his neck, fingers brushing through his hair in a soothing gesture.
“Easy. Try and take deep, even breaths.” At Reimei’s soft voice he shudders, eyes squeezing closed as he tries to slow his wildly beating heart and bring his erratic breathing under control.
Long minutes later he can take normal breaths again and he feels a gourd being pushed into his hands.
The water is cold and crisp and he spits out the first mouthful to rinse away the taste of bile before downing the rest.
Finally, he glances uneasily at his teacher, finding her eyes once more back to normal. They’re fixed on him, a hint of sadness visible in their depths.
“I apologize, Genya-kun. This is not how I wished for this to go.” She says. Slowly, she pushes herself to her feet and offers him her hand. There are faint traces of blood left under her nails and smudged along her jaw, but the majority of it has been wiped away.
“If you would like, we can go back to the inn and I can explain. Or I can call the Master and have you reassigned.” She offers. Genya blinks up at her, uncertain.
“Explain what, exactly?” He manages to ask, his voice hoarse. Reimei tilts her head a little.
“Me.” She responds, gesturing briefly to herself.
He hesitates another moment before, slowly, reaching out to take her hand.
Genya doesn’t get much sleep that night, lying awake for hours thinking about what his Sensei had told him.
After they'd gotten back to the inn she’d sat down across from him in their shared room, poured tea for the both of them, and then fixed him with her sharp green eyes.
“I hope you understand, Genya-kun, that what I am about to tell you must never leave this room.” She said. He swallowed thickly, but nodded, determined. Reimei had watched him for another moment before letting out a deep sigh.
“The two of us share a unique ability; we can consume demons without adverse side effects. Though I imagine the origins and reasons for such are a little different.”
“Origins?” He couldn’t help but ask, and for just a moment her eyes flicker, an unbearable sadness reflected in their depths.
“The circumstances of my birth are...complicated. However, because of that I stand on the border between humans and demons.” Here she held up her left hand, palm up.
“You are fully human, Genya-kun. You sustain yourself with regular food and water, and only consume demons in order to enhance your natural strength.” She holds up her other hand to mimic the first.
“Demons, despite once being human, can only sustain themselves by devouring humans. They also give up their ability to walk in the sun for enhanced speed, strength, and healing abilities, as well as an unnaturally long lifespan.” She brought her hands together, like she was cupping water in her palms.
“I stand somewhere in the middle. While I can survive mostly on human food, there are times when I must feed on demons. And I do not do it to enhance my strength, but to survive.” She let her hands fall to pick up her tea cup, taking a slow sip before continuing.
“Despite all of that, I am not a demon. I can walk in the sun and nichiren blades do not affect me any more than normal ones. However, I am not entirely human, either. My regeneration speed, for example, while not instant, is much faster than a normal persons.” Here, she extended her left arm and pulled up her sleeve, revealing a set of three jagged claw marks on her forearm that stand out starkly against her porcelain skin.
“The demon I ate earlier this evening did this to me. As you can see, it is already scabbing over. By tomorrow morning it will most likely be gone entirely.” She said.
Genya couldn’t help but stare, transfixed. The wounds indeed looked several days old instead of their actual age of barely an hour and he felt a kind of morbid fascination at the sight of them.
“I was assigned as your teacher because you can do something similar. By consuming demons, you will gain not just their strength, but their regenerative abilities, as well. Depending on the demons you eat, you may even be able to go head to head with a lower moon by yourself.” She explained.
“People like you, Genya-kun, are actually quite rare. Even rarer than marechi. You see, though all humans possess the ability to do so, consuming the flesh of a demon usually has only two results. Either the human in question crumbles away when the demon's power runs out, or they go mad with the demon’s blood and start attacking other people.”
“They turn into demons?” Genya asked, horrified. Reimei shook her head.
“No, they become something much worse. They lose all of their cognizance, devolving into little more than wild beasts that attack anyone and everything indiscriminately. But, unlike real demons, they gain nothing from eating humans. Sometimes, they are caught by human authorities and executed, but more often than not their madness drives them to start eating their own bodies, killing them in the process.”
Genya swallowed thickly, horror making his chest tighten.
“As you might think, my own circumstances notwithstanding, for this reason eating demons is strictly forbidden by the Demon Slayer Corps. And almost all information on consuming demons is kept a closely guarded secret, hidden behind as many layers of taboo and regulation as Ubuyashiki-sama can manage. My own movements, while not restricted, are also kept under wraps. To most, I am simply a particularly efficient Kinoe who dislikes company. Ubuyashiki-sama and Kanae-san are the only two who know of my true nature, partly to keep me safe from other members of the Corps, but mostly to prevent this information from reaching Muzan.”
They had fallen into silence as Genya had processed everything Reimei had told him, mulling over the implications quietly until something occurred to him.
“Won’t you get in trouble for telling me all this?” He asked, curious. Reimei shrugged.
“Maybe, but I told you, as my student it is my responsibility to take care of you. This is information you need, so I’ll deal with the consequences when I come to them.” She explained. Genya had blinked, feeling his chest tighten at the conviction in her tone.
Now, Genya stares into the still darkness of their room, listening to his Sensei’s soft, even breathing, and feels his mind finally settle.
It’s odd, he thinks, how comfortable he is. Not since he was living with his mother and siblings had he felt like this, and for it to happen in such a short time is unusual for him. But there’s just something about Reimei that puts him at ease, makes him want to curl up and huddle in her shadow like a small child, so assured is he of his safety in her presence.
Even when she'd been staring him down in the alley, crimson eyed and bloody, he hadn’t been afraid of her.
Maybe it’s because he hadn’t felt any hostility from her, or because of her constant assurances that it’s her duty to look out for him, but as he finally closes his eyes and slips into a dreamless sleep, he thinks that he might have been incredibly lucky getting her as his teacher.