The residents of Butterfly Mansion came to see Reiji off. The ghost of Kanae was right there as well, unbeknownst to any of them.

Their souls were tinged with bittersweet sadness, having grown used to his presence on some level. Butterfly Mansion would be a lot quieter now without the sound of a bamboo flute echoing through it every afternoon.

Shinobu still had that unknown emotion Reiji couldn't quite place mingling with the perpetual anger inside her. Whatever it was, it wasn't enough to stop her from giving him a smile which he returned.

His basket hat remained tucked under his arm for the time being so he could say goodbye face-to-face. His pale silver hair, which was usually messy from always being in a basket, had been neatly combed just for the occasion.

Aoi walked up to Reiji and handed him something long wrapped in fine silk.

"Shiki-san, before you leave, please take this."

Reiji curled an eyebrow at her but accepted the gift with a grateful nod.

"Thank you, Aoi-san." Reiji unwrapped the silk to reveal a familiar bamboo cane inside. "Oh, it's my old sword cane! You fixed it?"

"Not exactly," said Aoi. "The blade was bent beyond repair, so I had it replaced."

Curious, Reiji pushed up the handle of the hidden sword to reveal a deep blue blade inside.

"Such a beautiful blade," said Reiji. "But is this really alright, Aoi-san?"

"It's fine," Aoi insisted. "That's a nichirin blade, capable of slaying demons. All demon slayers get one after passing the final selection, but I've since withdrawn from the front lines to help at Butterfly Mansion instead. It'll be put to better use in your hands, Shiki-san."

"I'm grateful for such a wonderful gift." Reiji bowed deeply to Aoi. "I'll be sure to practise with this in between my meditations."

Unbeknownst to anyone other than him, Kanae clasped her hands in joy.

"Oh, this makes things so much easier!" she said. "I thought we were going to have to steal a nichirin blade at some point. Thank you, Aoi-chan!"

Aoi returned Reiji's bow, unable to sense the ghost trying to pat her head and going straight through it.

"Just be careful, Reiji-kun," said Shinobu, equally ignorant to the ghost of her sister. "It'd be a shame if you got yourself killed in training before you could behead even a single demon."

"You take care as well, Shinobu-chan," said Reiji. "I want you still alive to congratulate me when I become hashira too."

"Confident, aren't we?" Shinobu teased. "Let's see if you still have that attitude after a year of contemplation."

"If I ever have doubts, I'll just imagine you chastising me," joked Reiji. "That's sure to get me back on track."

The unfamiliar emotion in Shinobu flared up again, though her expression refused to change.

"Maybe I should chastise you right now then." She stepped closer to him, her deep purple eyes staring into his. "So you can have a reference in your head."

"Not a bad idea." Reiji bent down slightly to meet her challenging gaze with his own pitch black eyes. "But I doubt I'll ever forget a gorgeous face like yours anytime soon."

"Is that so?" Shinobu reached up to poke him on the cheek. "Or are you just saying that to escape a well-deserved scolding?"

"Oh, by all means, scold me all you like." Shiki touched the back of Shinobu's hand and gently pressed her cool palm against his cheek. "Just be careful what you say now, because I won't soon forget it either."

That mystery emotion inside Shinobu drowned out almost everything else within her, allowing only anger and irritation to poke through.

"You cheeky, cheeky man." She pinched his cheek and dragged his face all the way down to be level with hers. "That silver tongue is going to get you into trouble someday, you know?"

"Probably," said Reiji, his tone still matching her calm despite the pain in his cheek. "If only there were a way to tame it."

"Careful what you wish for, Reiji-kun." Shinobu hardened her pinch. "You might just get it."

"Oh? Who's going to grant it to me?" Reiji just grinned in response to the pressure between her fingers. "You, Shinobu-chan?"

"You know, I just might…"

Kanae glared at Reiji, then at Shinobu, then back at Reiji again.

"Okay, what exactly is going on between you two?!" She turned to the other members of Butterfly Mansion, none of whom could sense her. "Aren't the rest of you going to say anything?!"

The child trio of Sumi, Kiyo, and Naho huddled close to each other with their little button eyes gleaming with innocent fascination.

Aoi's face had turned a bright scarlet. Once again, it was up to her to break the tension.

"Well, uh, take care, Shiki-san!"

"Hm?" Reiji broke eye contact with Shinobu, prompting her to let go of his cheek. "Oh, of course! Thank you again for the sword, Aoi-san."

Reiji bid his goodbyes to the ladies of Butterfly Mansion and put his basket hat back on. Kanae walked beside him, her transparent face fixed in a disapproving frown while his remained inscrutable under the basket hat.

They made their way into town, where Reiji found a secluded alleyway away from the morning commotion. After making sure no one was watching, he promptly collapsed against the wall. The bamboo cane shook so hard in his grip that he could almost feel the hidden nichirin blade rattling inside.

"Holy fuck that woman is not good for me," he whispered under his unsteady breath.

Kanae, the only one there to listen to him, crossed her ghostly arms over her chest.

"Is this going to be a trend between you two?" Kanae asked. "Act all cool and suave when together then have a heart attack the moment you're away from each other?"

"At this point it's a game of who gets flustered first, and I don't intend to lose to the pint-sized princess."

'Wait.' Reiji caught onto an implication in Kanae's words. 'Does Shinobu get flustered like this when I'm away too?'

A gaggle of hungover men stumbled into the alleyway before Reiji could voice his question, forcing him into silence.

When they passed, Kanae was the first one to speak.

"So, where to next?" she asked. "We're going to need somewhere private to train you."

"There's a place I know about three days away from here by carriage," said Reiji. "There should be a pious merchant somewhere willing to give me a lift."

The smile returned to Kanae's face.

"Let's go find one then!" she said. "Let's both work hard together from now on, alright?"

Kanae stared at the rundown temple.

Time had buried it in a thick layer of foliage that made it blend into the surrounding forest. Twisted weeds strangled the mossy stone and half-rotten wood that hadn't been cleaned in at least a century. Tall grass had long grown over the dirt path that led to it, ensuring that none would ever intrude upon the once sacred ground now left in perpetual decay.

"...This is the place you were talking about?" Kanae asked. "Is it really okay to live in a place like this?! It looks haunted!"

Reiji ignored the irony of a ghost getting worked up about a possible haunting.

"Don't worry, I already appeased all the ghosts that used to reside here." Reiji trudged towards the temple through a sea of overgrown grass and dead leaves. "It'll be just you haunting this place now."

"Are you going to be fine though?" Kanae asked. "I mean, what about food, water, and shelter?"

"The inside of the temple should still be insulated enough to provide shelter." Reiji left his shoes at the door as he entered the temple, taking note of the miraculously intact ceiling. "There's a well behind the temple that I can get water from and there's a town two hours from here on foot that I can restock from once my current supplies run out."

Kanae looked unconvinced, but nodded anyway. "If you say so, I suppose."

"Have a little faith." Reiji unpacked his meagre belongings, including some flint for the fireplace. "I've survived four years of wandering on my own. Just having a roof over my head is already good enough for me."

Kanae did the maths in her head. "You've been living on your own since you were twelve?"

"Twelve or thirteen." The fireplace slowly flickered to life, fuelled by the dead leaves already inside and a little tinder from Reiji's pack. "I'm turning seventeen next month."

"You'll be the same age as Shinobu then?"

"Apparently so," said Reiji. "Are you going to visit her while I sleep?"

"Probably." Kanae turned her gaze to the window. "You should get some rest, Reiji. I'll start your training tomorrow."

Reiji nodded and unrolled a long cloth to use as a futon. "Thank you again for choosing to train me, Kanae."

"Don't thank me too soon." The gentle smile on Kanae's face took on a sinister edge. "I can be a strict teacher, you know?"

Kanae wasted no time making good on her word the next day, and every day after that.

First came physical conditioning with a focus on flexibility, speed, and agility. It mainly involved a lot of stretches, repetitive movements, and holding contorted positions for long periods of time.

While several metres in the air.

Hanging from tree branches.

Sometimes upside down.

Kanae apparently wanted to instil the fear of God in him should he make even the slightest slip, and it was working.

If he ever fell short by too far, she'd straight up possess his body and do it for him. Even though she was the one in control, he could still feel all the pain of getting twisted every which way in positions no human body was ever meant to make. Far too often she would forget that she was possessing a man's body with bits where here old one had none and end up making moves that hurt him far more than it did her.

Every little movement she made with his body was pounded into his muscle memory while the agony it caused wouldn't fade from his regular memory anytime soon either.

After two weeks of gruelling training, Kanae sat his sore, exhausted body down to explain the basic concept of Total Concentration Breathing and its many styles.

By controlling one's breath, demon slayers could apparently accelerate their heart rate and blood circulation to their muscles, making them theoretically as strong as a demon whilst still human.

Different breathing styles focused on enhancing different parts of the body to utilise their sword forms-the attacks Kanae was so eager to shout out during her first fight in his body.

"Flower Breathing is focused on agility rather than raw strength," Kanae explained. "By directing blood flow into the eyes, its users can also raise their kinetic vision and visual acuity-though overdoing this can burst blood vessels in the eyes and cause blindness. This breathing form was created by a woman with women's strengths in mind, but that doesn't mean a boy like you can't use it too!"

"Speak for yourself." Reiji massaged his sore thighs. "Those splits you did in my body hurt like hell. Also, I'm not sure about risking my eyesight for this. Whatever advantages I can get from straining my eyes to bursting can't be more useful than my ability to see spirits."

"You're not wrong." Kanae tapped her chin in thought. "You could try creating your own breathing style too, you know?"

"That's a thing?"

"Of course!" Kanae shook her fists together in a supportive gesture. "New breathing styles are created all the time by slayers tweaking existing ones. Insect Breathing, the style Shinobu-chan uses, is derived from my Flower Breathing. You could go down the same path."

"I do like the idea of being faster and more agile than my opponent." Reiji racked his mind for possibilities. "But perhaps I don't need to put as much focus on it as you did. Since I'm more muscular than you were and a little taller, I might as well make use of that fact. Maybe I can adjust your breathing style to be a more even balance between speed and power?"

Kanae beamed at him. Her transparent face looked like a glowing moon outshining the sun in broad daylight.

"Now you're thinking like a demon slayer!" Kanae gave him a pat on the back which was just her swinging her intangible hand through his torso. "Keep it up and you'll be a hashira in no time!"

The next several hours with Kanae was spent learning the basics of Total Concentration Breathing and practising sword forms on bamboo. One particularly ridiculous thing she had him do was kick a tree hard enough to cause leaves to fall then slice every single one of said leaves in half before they could hit the ground.

Kicking the tree over and over again hardened his leg bones and muscles. Having to watch for every falling leaf improved his kinetic vision. Running, jumping, and occasionally backflipping off the tree to reach all of them trained his speed and agility. Actually slicing them mid-air honed his instincts for aligning the sword's edge and sharpened his hand-eye coordination.

It was an effective, if not profoundly annoying and tiring exercise.

Once Reiji found himself in a steady rhythm, Kanae left him to practise by himself while she teleported to haunt Shinobu while she went on a hashira mission.

She returned to the mostly abandoned temple late in the evening to find Reiji still training.

Halved bamboo trees littered the makeshift training grounds, and much of the tall grass around him had been inadvertently cut down by him practising his swings.

"Well, you've been a busy butterfly," said Kanae as she approached him. "Don't worry if you haven't learned Total Concentration Breathing yet. It usually takes time for someone to really get the hang of it."

"I think I've got the basics down at least." Reiji sheathed his nichirin blade back in its cane sheathe. "By combining the forms you taught me with the sword dances I used to do for rituals, I might be able to create a breathing style of my own."

"That's wonderful!" Kanae was about to give him another pat on the back when something about him made her pause. Her droopy eyes looked up and down his chest and basket-covered head before widening in surprise. "Wait…Reiji, are you using Total Concentration Breathing right now?"

"I am," said Reiji. "Is…is that bad?"

"What? No, but how long have you kept it up?"

"Since about an hour after you left, why?"

Kanae quickly did the maths in her head, which only made her look more perplexed.

"Reiji, that's almost seven whole hours," she said. "Are you feeling alright?"

"I mean, I'm pretty damn tired and sore all over but aside from that I'm fine." Reiji grew concerned at how surprised Kanae seemed to be. "Is keeping Total Concentration Breathing up for too long bad? Should I stop?"

"No, don't stop!" Kanae beamed at him, her earlier concern vanishing in an instant. "You're doing wonderfully! The longer you can keep up Total Concentration Breathing, the greater your stamina and baseline physicality will improve. I'm just surprised, that's all. Most demon slayers only use it when executing their forms. Constantly having it on is an advanced technique only especially skilled demon slayers like the hashira can use. You've made amazing progress in one day!"

Reiji felt his cheeks heat up at the praise. He hoped that Kanae couldn't see them turn red through the holes of his basket hat.

"I have an advantage over other trainees, I think," he admitted. "Back at the temple I used to live in, I had to keep myself in a constant meditative state that prevented ghosts from forcibly possessing me outside of channelling sessions. A lot of it boiled down to controlling how I breathe, so I was able to tweak it into something resembling a breathing style."

"How clever!" Kanae clasped her hands together, clearly pleased. "Is that how you kicked me out of your body back then?"

"Yes, I activated it after it became clear you were trying to take over," said Reiji, causing Kanae to look away with downcast eyes like a guilt-stricken puppy. "I used to keep it up at all hours of the day, but since I left the temple it's been easier for me to just ignore ghosts instead. I got back into the groove of it pretty easily by also applying the techniques you taught me."

"Does that mean I won't be able to possess you from now on?"

"No, I already know what your presence feels like. If I sense that it's you inside me, I won't kick you out. That is, unless you get any more bright ideas about talking to Shinobu."

Kanae held up her hands in surrender.

"You win on that matter, Reiji." There was clear resignation in her voice. "But what about other ghosts? If we come across the ghosts of some other former hashiras, do you think they could possess you to fight as well?"

"It's possible if I allowed them to, but I'd rather not risk it if at all possible," said Reiji. "Not every ghost will be as compatible with my spirit as you."

"You mentioned our spirits being compatible before," said Kanae. "Were you just flirting or was that supposed to actually mean something?"

Reiji cleared his throat, his cheek reddening under his basket hat again for a moment.

"Spiritual compatibility is a real thing." He sat down and leaned against a now nearly leafless tree full of splintered bark from countless kicks. "Being spiritually sensitive allows me to be possessed by ghosts, but the relative spiritual power of me and the possessing ghost determines how well things turn out."

"You lost me there," said Kanae. "What do you mean by that?"

Kanae sat in front of him, her pale violet eyes looking at him with curiosity as he pondered for the right words.

"Think of me as a half-empty glass of water," he said after a moment of silence. "The glass is my body while the water is my soul. The volume of the water represents my spiritual power. Getting possessed by a ghost is like adding ice cubes to the glass. The greater the spiritual power of the ghost, the more ice cubes get added. An ideal possession happens when enough ice cubes are added to chill the entire glass without causing the water to spill out. Your spiritual power is more or less equal to mine, allowing us to both think clearly and move fluidly when you possess me. So much so that at times it becomes difficult to recognise who's in control."

"I think I get it," said Kanae with a nod. "What happens if you get possessed by a ghost with weaker or stronger spiritual power?"

"If it's a ghost with weaker spiritual power then they'd be little more than a voice in the back of my head. I could allow them to speak through me, but they'd be incapable of any advanced motor functions. Things only get really bad if I'm possessed by a ghost with greater spiritual power."

Reiji shifted where he sat. He disliked even entertaining the thought of getting possessed by a stronger spiritual force, but Kanae should know how his abilities worked. They were going to be fighting together for the foreseeable future, after all.

"When I get possessed by a stronger spirit, parts of my own soul get pushed out to make room," he explained. "Like how adding too much ice to a glass of water can cause it to spill out from the brim."

"What do you mean by that?" Kanae sounded concerned. "What gets pushed out of you exactly?"

"It varies depending on the discrepancy between me and the ghost's spiritual power. The greater the discrepancy, the greater the loss. It could be something small, like a long standing habit or a personal quirk. But if the discrepancy is high enough then it could also be the way I feel about certain things or recall certain events. A cherished hobby can become meaningless, a favourite food may lose its flavour, and memories that once brought me comfort could fade or even disappear entirely. I'm…not sure if this is because of the possessions or not, but I can't really remember what my birth parents look like anymore."

"That's terrible!" Kanae clasped her hands over her mouth in horror. "Is there any way to prevent that from happening?!"

Reiji shook his head.

"It's all up to luck. Whatever I lost may eventually return to me after the possession ends, but not always. Half the time I wouldn't even be able to remember what it is I lost. Honestly, after having been possessed by so many powerful spirits, I'm not really sure how much of my original personality is even left inside my soul."

Kanae looked horrified as she recalled all the times she'd casually possessed Reiji over the course of their training.

"Is…is it really safe for me to keep possessing you?" she asked in a shaky voice filled with unfounded guilt.

"It should be fine if it's just you," Reiji assured her. "Since our spiritual power is similar, you're able to possess me without any ill effects."

"Are you sure?"

"Positive," said Reiji. "Though let's put a pin on channelling the ghosts of other hashira. Spiritual power is largely determined by an individual ghost's personal willpower and how long they've been bound to the earth after death. The more ancient the ghost, the more time they've had to grow in spiritual power. Generally speaking, it's a bad idea for me to channel any spirit older than a century."

"Let's avoid doing that then." Kanae started to calm down, and the gentle smile returned to her face. "You should rest now. You've already made more progress in one day than some trainees do in a month."

"I have no objections to that." Reiji slowly rose to his feet, stretching his back as he did. "I should probably keep up my Total Concentration Breathing even when I'm asleep, right?"

"If you can," said Kanae. "Do you want me to wake you up if you ever stop doing it?"

"That sounds like it'd be a pain in the arse for both of us," said Reiji dryly. "But it'd be appreciated. I want to be as strong as possible when the time comes for me to fight actual demons. Gods willing, I may actually get the chance to avenge your death someday."

Kanae let out a soft chuckle.

"You're talented, no doubt about it, but you're still a long ways away from defeating an Upper Moon."

"A what now?"

"They're a group of powerful demons who operate directly under Muzan Kibutsuji's orders," Kanae explained. "But you needn't worry about them for a while. Just focus on your training and you'll do great."

"If you say so."

Reiji returned inside the temple, where he made a simple stew of dried meat and mushrooms. After lighting a little incense and bowing before the bowl of stew in offering, a ghostly version of it appeared to Kanae for her to enjoy as well.

It wasn't quite the same eating with a living, breathing person, but it was close enough to make the decaying temple feel a little less empty.

"By the way," Kanae spoke through a mouthful of ethereal stew. "Have you figured out any forms for your new breathing style yet?"

"I haven't gone quite that far yet," said Reiji, his basket hat set to one side so he could eat. "But I've come up with a rough idea of what I want to accomplish with it."

"Oh, do tell!" Kanae spoke like a housewife trying to get details on the latest gossip, and Reiji couldn't help but smile at the absurdity of it.

"I've been thinking about the way you and Shinobu move," said Reiji. "Both of you are light on your feet and generally fast. I'm not sure if I can achieve a similar consistent movement speed as you two, but I think I can get somewhere close then supplement it with small bursts of speed scattered in each of my forms. Like a phantom appearing in the dead of night only to vanish into thin air."

"Glad to have given you so much inspiration," said Kanae. "Just let me know if you need any help coming up with names for your forms. Remember, they must be catchy and easy to shout in a fight!"

Reiji rolled his eyes. "Is that really necessary?"

"Of course!" Kanae insisted. "Breathing styles are a proud tradition among demon slayers with a rich history. By saying its moves aloud when you use them, you are honouring the legacy of all the swordsmen who came before you to make demon slaying possible."

"Huh." Reiji paused to think about what Kanae said. "I never thought of it that way."

"But before we get to the form names, we must think of a name for your breathing style so we can keep with the theme." Kanae gave him an expectant look. "Have you thought of one yet?"

Reiji needed but a moment to think before replying.

"How about Ghost Breathing?"

Taisho Era Secret!

Reiji's favourite food in the whole world is apples! The happiest memory he still has is him eating freshly picked apples under an apple tree on a rainy day.