Warnings: Rengoku Volume 0 spoilers (A bonus one-shot about Kyojuro's first mission as a slayer.)

It's unusually hot and humid the day you meet Rengoku Kyojuro.

You wipe the sweat from off your forehead with the back of your hand and glance towards the setting sun on the horizon.

Such strange weather... you think to yourself as you begin the trek back to Oyakata-sama's place with the herbs you picked for his medicine. It shouldn't be this hot and humid this time of year.

Picking up your pistols, which are lying in the dirt next to your feet, you steady yourself before taking off at an incredible speed down the mountain. The sun was setting and you had to hurry back before any demons came out.

You leap over fallen branches and stones with practiced ease, white haori fluttering out behind you. Animals squeak and chitter at you as you speed past, annoyed at you for disturbing them. A cloud of dust is kicked up as you rapidly swerve left. Through the trees, Oyakata-sama's residence comes into view but it's painfully small and you can barely see it unless you squint. Your dove cooed a warning overhead, urging you to go faster.

"Twenty minutes until nightfall, coo, coo!"

"Thanks!" you shout back as you jump over an exposed tree root just in the nick of time. You land on your feet with a loud "oof" before shaking yourself off and continuing down the mountain.

"Slow down!" your dove calls. "I can't keep up with you!"

"Then you haven't been training enough!" you huff as you glance left and right for the path you had worn from multiple trips up and down the mountain.

There it is.

Swerving right, you find yourself on the familiar, well-worn, and beaten path you had created. "If you can't keep up with me, that's saying something!"

After all, I am the weakest person in the entire Demon Slayer Corps.

The rest of the path is clear of any obstacles, so you sneak a glance towards the sun setting off in the west. The top half of it was still visible above the horizon, providing you with enough light to see.

Good. I think I have enough time to get back safely.

The ground evens out beneath your feet as you finish descending the mountain. Taking a few moments to catch your breath, you look up to your dove, who guides you back to your residence.

It is a two-story Western-style building in the style of a Spanish villa with arched doorways, high windows, and slanted roofs with terracotta roof tiles. You leap up the front steps and push the front door open, heading straight towards your laboratory. There is a small cedar box in the corner of the room, tucked away from any sunlight, which you run towards.

The inside is filled to the brim with ice. You pull on a pair of gloves and dig through the box for a bit before finding what you were searching for.

It is a small, squat glass bottle. A topper prevents its contents from spilling out. They were eye drops.

Good, it's not frozen. It's chilled, but the medicine inside hasn't turned to ice. It's exactly as it should be.

Closing the lid of the icebox, you hurry over to a countertop and grab a mortar and pestle, where you grind up the herbs you had gathered earlier into a paste. The strong medicinal smell makes you wince and scrunch up your nose, but you are used to it by now.

Grabbing some wrapping paper, you split the medicine up into seven doses and tie each off securely with some cord.

"I can't keep Oyakata-sama waiting for much longer," you mumbled as you grabbed the eyedrops, packages, and your medical kit before running out the front door. You swiftly slam it shut behind you and make your way to his residence, your dove leading you overhead. The sun had long since gone down and the sky was a deep navy blue now. Stars dotted the night sky like small sequins.

I hope there aren't any demons nearby...

The gates surrounding Oyakata-sama's residence come into view around the corner. A Kakushi standing guard recognizes you and opens the doors.

"Good evening, (Y/N)-sama."

"Good evening to you too," you reply as you dash across the garden. Oyakata-sama is sitting on the engawa, surrounded by his wife and five children. You immediately drop to your knees and bow your head.

"I apologize for the wait, Oyakata-sama. I am now here with the medicine as you requested."

He turns towards you with a gentle smile, not unlike the one he would show his children.

"There is no need to apologize, (Y/N). You are perfectly on time."

You take that as your cue to get up. Stepping onto the engawa, his children clamor over one another to be the first one to greet you, wide smiles of excitement stretching across their faces.

"Kids, stop that at once," scolded their mother, Amane Ubuyashiki. "That's very rude of you and you are making (Y/N)-san uncomfortable."

You chuckle as Kanata snuggles up to you, hugging your legs. "It's alright, Amane-san. Your children are very polite and adorable, so I don't mind at all."

She turns towards you, dipping her head as a welcome. "I'm glad to see you in good health, (Y/N)-san. We owe our eternal thanks to you."

Nichika and Kuina hug you around the waist before leading you by the hand to where Oyakata-sama is. You sit with your legs tucked neatly underneath you, fidgeting uncomfortably every few seconds.

You give their middle child and only son, Kiriya, a soft head pat and a warm hug. He smiles and leans into your touch.

"How have you all been?" you ask.

"Very well thanks to your efforts, (Y/N)," said Oyakata-sama. "Your medicine is working wonderfully."

You bow, fingertips brushing each other. "I am glad to hear that it is working, Oyakata-sama. I have brought the medicine for this week and I hope it continues to work."

You pull out the seven bundles of medicine that are crammed into your already-full medical kit.

"This is the medicine for this week. As usual, please take this once per day with water as a tea on an empty stomach. In addition, here are the eye drops. One drop in each eye every night to slow down the progression of your father's blindness. Remember to keep the eye drops in the icebox at all times or somewhere cold and dark, but make sure it does not freeze."

"Understood," said Kiriya as he took the medicine and handed them to his mother, who promptly stood up to store them away.

"I've always wanted to know this, (Y/N) nee-san, but how come the eye drops have to be kept cold?" asked Kiriya. His four sisters nodded in agreement.

"Well, some medicines need to be kept in cold temperatures to keep them at peak effectiveness," you explain. "If they are at room temperature, then they can begin to lose their effectiveness or worse, even become toxic. We don't want that, do we?"

They shake their heads.

"But how do they become toxic or lose their effectiveness?" asked Kanata.

"That is due to things called bacteria and germs. They are the main cause of most diseases in today's world and they are present everywhere, such as on your hands."

They examine their hands closely.

"You won't be able to see them like that since they're too small for the naked eye to see, but they are very destructive for their size.

"Under extreme temperatures, bacteria and germs cannot survive so they die off. In the case of your father's medicine, chilling the eye drops will kill off all bacteria and make sure the medicine works as it should. Extreme heat can also kill them off, but it is seldom done with medicine because it can also decrease the effectiveness of it.

"However, if you leave the medicine out at room temperature or in direct sunlight, then that is a good temperature for bacteria to grow. As a result, the effectiveness of the medicine will go down since there are more bacteria and if it is too much, it might even be toxic. Think of those times when you ate something that was left out for too long and your stomach started to hurt. Quite uncomfortable, wasn't it?"

They giggled at your last line. You wiggled your fingers and stuck your tongue out.

"I'm the evil bacteria who's going to eat you up! Hahaha!"

They screamed and moved away from you. Unfortunately, Kanata wasn't fast enough and you quickly caught her, tickling her sides and smushing your cheeks against the adorable girl.

"I- (Y/N) nee-san, not there! That tickles!"

"Do you surrender?"

"Yes, I surrender!"

You let go of her, but not before gently pulling at her cheeks and hugging her.

"I want to become a doctor now!" she said. "You make it seem so interesting!"

"I'll look forward to seeing you in the field later on then! If you have any questions, feel free to come to me. Your big sister will be more than happy to help you out!"

She beamed up at you, arms still wrapped around your waist.

"(Y/N), you are so young, but you have already done so much. Truly, we are honored to have a doctor like you."

"Thank you for your kind words, but I am simply fulfilling my duties as a doctor. There is no need to praise me."

Despite your humbleness, you can feel the beginnings of a blush creeping up your cheeks at Oyakata-sama's words.

The sound of footsteps approaching makes you turn. The Kakushi from earlier bows deeply towards Oyakata-sama before turning to face you.

"(Y/N)-sama, there is someone who needs to be treated."

Your expression hardens. "Understood. Take them to my estate and have them rest in the infirmary. I'll be there in just a moment."

He nods before running off. You bow once more before standing up.

"If you'll excuse me, Oyakata-sama, I will be taking my leave now."

He nods. You say goodbye to his children and Amane with the promises of visiting again sometime soon before you are quickly dashing across the garden and out of the gates to your estate.

Your manor was very close to Oyakata-sama's residence, only a five-minute walk away in fact. As the Ubuyashiki family doctor, you had to be ready at a moment's notice in case his disease suddenly got worse.

The light in the infirmary is on. You can see it through the window as well as three shadows moving around.

Good. The Kakushis must be helping them get ready.

You enter through a side door. Upon entering the laboratory, you take your haori off and grab your white smock and tie it around you. It is made of a thick white fabric that goes down to your knees and covers most of your body beneath your neck.

You spot one of the Kakushis heading towards you.

"What happened?"

"Nothing too bad," he responded. "He's a new slayer who just completed his first mission and aside from the typical scratches of battle, he's alright. There's something up with his ears, though."

His ears? That's not a common battle injury...

"His name?"

"Rengoku Kyojuro. He's the son of Rengoku Shinjuro, the current Flame Pillar."

Rengoku. 煉獄. Meaning: "Purgatory".

It sends a shiver down your spine.

Turning around, you push the door that separated the infirmary from the laboratory, and you get your first glimpse of the slayer in question.

You notice his hair first. It is a brilliant gold with the tips of it being a flaming red. Long and fluffy, it cascades down his back in waves with a small section of it tied back in a ponytail at the back of his head.

It reminds you of the colors of the rising sun and shrimp tempura.

Then you notice his eyes.

They take your breath away. An unusual color; the same as his hair. You feel as if his piercing gaze is staring into your very soul. His eyelashes are long and fluttery, sending a twinge of jealousy through you.

Wide-set and unblinking, he stares forward at you unflinchingly, almost as if he is challenging you. You are reminded of the still and unblinking eyes of dolls which gaze straight ahead into nothingness.

It unnerves you a bit. You feel like he can see everything you have done in your life, including your sins and regrets.

"Hello there!" he booms, distracting you from getting lost in his eyes. "Are you the doctor who is going to treat me?"

He's quite loud, you think to yourself as you nod. "Yes, yes I am."

There's no response from him. He tilts his head to the side and blinks at you like a fluffy puppy.

"Did you just say something? Because I didn't hear anything."

You raise your eyebrows, surprised he couldn't hear you.

Looks like the Kakushi was right about his ears. My best guess is a ruptured eardrum or two.

You take a seat next to him. Looks like you'll have to speak louder than you're accustomed to.

"Yes, I am the doctor who will treat you. My name is (Y/N) (L/N). It is a pleasure to meet you," you said again with more volume this time. "I heard your ears were injured during your mission."

"That's true," he said. You avoid looking into his eyes and busy yourself with grabbing an otoscope off a shelf hanging on the wall.

"Please hold still for a second."

Shining it into his ears, your suspicions were confirmed. For both ears, the eardrum was ruptured.

"Both of your eardrums are ruptured," you explained after you returned the otoscope to its spot. "The vast majority of ruptured eardrums typically heal by themselves within three months, but I'll give you some medicine to prevent infection."

You got up and opened the door to the laboratory, where you also stored medicine. As the door swung shut behind you, you could hear him talking to the Kakushis.

"Who is she? She seems so mature and elegant!"

"She's (Y/N) (L/N)-sama, the head doctor for the Demon Slayer Corps. She is also the doctor for the Ubuyashiki family, handpicked by Oyakata-sama himself, and the one who gives basic medical training to all Kakushis."

"Wow, that's incredible!"

"I know, right? She's quite an amazing woman."

You smile to yourself as you find the ear drops and acetaminophen you were searching for. The door creaks behind you as you shut it.

"Take these ear drops twice daily for ten days. To prevent infection, you should also try not to get water in your ears when you are bathing," you advised. "I'd recommend using a shower cap or water-repellent earplugs. If it hurts or starts to hurt, take one of these pills"- you shake the bottle of acetaminophen- "daily until the pain stops."

He listens to everything you have to say with dedicated attention and a nod after each sentence. The bright smile never leaves his face.

"I just explained a lot to you. Do you have any questions?"

"I do! Could you tell me a bit more about yourself?"

You freeze. Why would he want to know more about you?

Which is exactly what you ask.

"Why? Is there something that interests you?"

"Well, you seem to be around the same age as me, but you're already held in such high regard by the Kakushi and other members of the Demon Slayer Corps! For starters, how did you become a doctor?"

You smile. His booming voice, which had previously startled and scared you a bit, was now comforting to you in a sense.

Maybe because it reminded you of him.

"There's a little-known exam that you have to take if you want to become a doctor for the Corps. It's not an easy test. It's horribly brutal. The test spans several hours in length and not only does it feature a lengthy writing, reading, and multiple-choice section, there are also many hands-on tests that you have to pass, such as performing CPR, administering antidotes for poison, and more. There are also barely any breaks, as it's meant to replicate the experience out in the field. As a result, it's incredibly difficult to pass and most do not. The people who are taking the exam are few and far between, and the brutality of the exam makes it even harder."

"And you passed?"

A sly grin with a hint of pride spreads across your face.

"With full marks."

"Impressive, impressive! You must be incredibly intelligent! So many achievements at such a young age. (Y/N)-san, how old are you?"

The male Kakushi leaps to his side and slaps him across the face.

"Don't ask a lady that question, you dumbass!"

"Taro!" you scold sternly. He zooms back to his spot on the other side of the bed.

"Yes?"

"I will tolerate no such behavior from you. Go get some water for this young man. He must be thirsty after his exhausting mission."

"Yes, (Y/N)-sama."

After making sure he was out of the room, you sigh.

"I apologize about that. He's always been like this, but he has a heart of gold, really."

The male Kakushi's name was Taro. A former slayer, you had saved him while he was on the verge of death on a mission. The wound had rendered him incapable of fighting anymore, and he retired. Ever since then, he has stayed loyal to you and often helped out with the patients around your estate.

"No, no, it's alright! I respect his loyal and unwavering attitude towards you! Truly something worth commending!"

How does he have this much energy all the time?

"But about your question... I am the same age as you. I joined the Corps a little over a year ago."

"Even more impressive! May I ask you some more questions?"

You know you're in for a long night, but you don't mind. Not at all.

»»————-　♔　————-«

Yawning, you glanced at the clock. 10:06 pm.

You had been talking with him for over three hours.

"Rengoku-san-"

"It's just Kyojuro to you!"

"Kyojuro, it's getting late. For your safety, do you want to stay the night here? It will be much safer than attempting to walk home in the darkness. I'll send a message to your father to let him know that you're alright."

"If you insist!"

Your dove cooed on the windowsill. You turned towards him and relayed your message to him.

"Go tell Shinjuro-san and Senjuro-kun that Kyojuro is alright. He'll be back tomorrow morning."

He ruffled his feathers before taking off, looking like a shooting star against the indigo sky.

"You have a dove instead of a crow?" asked Kyojuro. "Interesting!"

"Mhm. His name is Poyo and he's very intelligent."

But why do I even have him?

I never passed Final Selection.

"Taro-kun," you call out. You hear the clatter of dishes and the sound of footsteps rushing over. His head peeks out from the doorframe.

"Yes?"

"Can you help Kyojuro here get set up for the night? I need to light the wisteria incense."

"Will do."

Disappearing out of a side door, you pull some wisteria incense sticks out of your pocket and place a few of them in each incense holder pot around the house before lighting them. The sweet, musky scent of wisteria blossoms drifted throughout the courtyard and through the air as you blew the flame out, leaving only a wispy trail of smoke behind.

Your house, much like all the other Pillars', was surrounded by tall gates that were routinely locked every night for extra protection against demons. You jiggled the front door handle, making sure it was locked securely, before heading back inside and locking the doors behind you.

"Anything else you need me to do?" asked Taro as you stepped back inside. You shake your head.

"No, you've done enough,