3

"You need to be faster and more unpredictable. Don't give your enemies a chance to react."

We were on our way back after the mission in which I killed the Lower Moon Two. Kyojuro and I reached just in time to rescue the group of Demon Slayers that we were supposed to find and provide support to. Kanae and Shinobu requested to train under me on our way back. I could not find a reason to refuse so I agreed. It will make the return trip a little more fun anyway.

And so, I danced with the sisters and Kyojuro, who would never say no to any form of training.

I can see why Kanae became a Hashira. She has natural born talent. Even after just a mere two years after she was first taught how to fight and use Breath Styles, her improvement is staggering. I took nine years to master the Dance of the Fire God. She took two years to master the Breath of Flower that she learnt from a book Urokodaki gave her, saying that it is a Breath Style the first user of the Breath of Flower had left behind. It is a Breath Style designed for women to use because not all Breath Styles are suited for a woman's physique. The first user of the Breath of Flower derived it from the Breath of Water after seeing how she was not suited to use the Breath of Water to its fullest effect.

"Stand up, you three. All of you said that you want to become Hashiras, did you not? Then why are all of you just lying there and not moving? Are you all just talk? Prove to me that you have what it takes to be a Hashira. Stand up."

If there's one thing I could not accept, it's giving up. Not giving up is what enabled me to master the Dance of the Fire God. If I had given up the moment I became breathless after just using the first form of the dance I could not have managed to finish the dance from sunset to sunrise alongside my father. My years of hard work was what enabled me to place myself at the starting line in the first place. My natural talent with a sword was a gift from the heavens, but a gift that I could not use to its fullest extent if it wasn't for my hard work in mastering the Breath Style Yoriichi left behind. Even so, I also had to put in a lot of hard work into perfecting the gift that I was given.

To me, giving up is never an option if I want to protect my family. That is why no matter what it takes, no matter how slim the chance may be, I will do whatever I can to protect them from Muzan.

They managed to stand up once more, ready to dance another round. Looking at the determination that they are showing, it is no wonder that they all ended up becoming Hashiras.

I held up my sword once more. I don't know how my presence will influence their lives, but I do hope it is for the better.

"Why are you still here?"

"Rengoku is assigned elsewhere and Shinobu is staying behind to invent more poison to use, so I guess that leaves the two of us~"

I scoffed and continued to walk ahead with Kanae walking beside me. Kyojuro and I have successfully completed our mission by escorting the group of Demon Slayers we rescued from the Lower Moon Two back to HQ. Kyojuro is assigned to another mission while I decide to go back to patrolling the area which I'm in charge of until another mission for me comes in. For some reason, Kanae decided to stick with me.

"If you're here to try and make friends, go elsewhere. I'm here to slay demons, not here to make friends."

"Oh my, oh my, saying that hurts my heart, you know? People of the same age should stick together! You are always so lonely whenever I see you around. And if you're not here to make friends, what about Rengoku?"

"I knew him before I became an official Demon Slayer. He doesn't count."

"Then how about you do the same for Shinobu and I?"

"For what? I don't have time to babysit anybody else. Go elsewhere if you want someone to teach you."

"But didn't you already taught us-"

"That was a one-time offer."

"You don't need to keep purposely pushing people out of your life, you know? I have no idea why you are always insistent on doing everything alone, but there will always be people who are willing to help you if you so much as stop and turn around, Haruto-kun."

Her words made me take a pause in my tracks. For some reason I cannot explain, her words ignited a sense of fury in my heart.

"Shut. Up."

I walked off, leaving her behind. There's no way I can involve others in whatever I'm doing. The whole point of me becoming a Demon Slayer is so that nobody from my family would ever need to involve themselves in this demon slaying business. It is so that nobody from my family will die. It is so that nobody from my family will ever need to pick up a sword.

If I have to do this alone, then so be it.

"Lord Muzan."

"Have you found what I tasked you to find?" Muzan asked without turning to look at the demon kneeling on the floor, more interested in his experiments than anything else. The only reason why he is gracing this particular demon with his presence is because this demon is a little special. It actually is able to withstand the effects of wisteria flowers, albeit only for a short while.

Still, this is already a big breakthrough on their end, to have a demon that is able to build up a slight resistance to wisteria. If all goes well maybe all demons in the future will be able to possess such resistance as well, something which will definitely be a huge blow to those pesky Demon Slayers.

"I'm sorry, Lord Muzan. I have failed to locate the Blue Spider Lily."

Muzan clicked his tongue in annoyance, finally looking up to face this somewhat special demon.

"Even then, you still have the gall to ask for more of my blood?"

"There is an area where demons dare not enter in recent years, for none who entered ever came out alive. I have checked and found out that a particular human settlement in that area is being actively protected by a Hashira. For the area to be so heavily protected by a Hashira, I believe that there is a small chance that the Blue Spider Lily can be found there, but as of now, I…"

"Are too weak to do so, am I right?" Muzan scoffed. In the next instant, tentacles emerged from within his sleeves and pierced into the demon.

"Fine, I shall grant you your wish. Do not disappoint me. Even if you cannot find me the Blue Spider Lily, go make yourself useful and kill a Hashira or two, then maybe you might be good enough to be a part of the Twelve Demon Moons."

The demon could not reply, still too busy screaming from having Muzan's blood forcefully injected into it.

She spotted it right away when she first saw him. The loneliness and strong sense of duty, it's all there in his eyes. They are about the same age, still children, and she doesn't why he constantly gives off the feeling that he doesn't want anybody else approaching him, as if he is afraid of forming bonds with others.

She doesn't like to see that kind of expression on anybody's face, so she tried to approach him in a cheerful manner, hoping that maybe she could be his friend.

He simply responded to her with as little words as possible.

But his spar with Urokodaki and Himejima is something she would never forget and she is sure it is the same for Shinobu. He is only about their age and yet he could go toe to toe against another two Hashiras all on his own. It surprised her further that he is already a Hashira when he's a year younger than her.

It's after witnessing that spar that she knows how far she needs to go in order to become a competent Demon Slayer, how much further she needs to climb up to become a Hashira.

"I think… I want to strive to be a Hashira too."

Seeing the way he fought as if doing an elaborate dance inspired her. It's then she made a vow that she will become a Hashira, so that other people will no longer need to experience the same pain and horror that she and Shinobu had gone through. She told him her vow with a smile. He probably doesn't remember that she even told him that, but she remembered what his reply was.

"Then do so. Don't just speak, do it."

He left right after he said that and she could do nothing but to watch the retreating figure of his back. He's not wrong. To become a Hashira you cannot just be all words, you need to prove it with your actions.

So, she trained, hoping to catch up to him someday, the person who inspired her to be a Hashira.

She learnt a little about the enigma when she was learning under Urokodaki. His name is Kamado Haruto, a prodigy that the previous Flame Hashira picked up from an unnamed mountain when he was on his patrols. According to Urokodaki, Haruto had invented a Breath Style all on his own through a dance he performed as a ritual ceremony. By the time Rengoku Shinjuro picked him up he had already mastered the Total Concentration Breathing and was able to behead a demon without prior training or guidance. He is also a natural with a sword, learning everything there is to know about it within a month and then passing the Final Selections with flying colours. A month later, he slain the then Lower Moon One, becoming a Hashira.

Everytime she looked at his back it felt that if anyone is favoured by the heavens, it is him. It's like in front of him, every amount of work you put in is useless. It's like he is born to surpass everyone, a being that is out of the reach of mortals.

She didn't see him all that much until about two years later when he and Rengoku arrived as their reinforcements. His back still seems so big and far. She saw how he effortlessly cut his way through the group of demons in his effort to locate the Lower Moon Two.

The distance she needs to close is still so big. She is still far from able to stand alongside the other Hashiras as their equal.

So, she requested for him to train her and Shinobu on their way back. By some stroke of luck, or maybe he was simply in a good mood, he agreed. Rengoku joined in as well and what turned out from that was a very one-sided beatdown Haruto gave them.

She could do nothing but lay on the ground in pain.

"Stand up, you three. All of you said that you want to become Hashiras, did you not? Then why are all of you just lying there and not moving? Are you all just talk? Prove to me that you have what it takes to be a Hashira. Stand up."

It was then she thinks she saw it, something in his eyes. That fierce determination to protect, she could identify it. It's the same look in her eyes whenever she thinks about her younger sister, whenever she made a silent vow to herself to protect her younger sibling from harm.

Maybe there's a lot more to the Fire Hashira then she thought.

She shamelessly bugged and stuck herself with him after they returned from their mission. Not just because she genuinely wants to be his friend, but also because if anybody can train her to be better without going easy on her, it is him. She doesn't like it when he puts on that unreadable and calm expression on his face all the time. He should really smile more.

"If you're here to try and make friends, go elsewhere. I'm here to slay demons, not here to make friends."

He saw through her attempts to befriend him right away. It didn't deter her. She pressed on, trying to get him to open up. It's when her words are starting to fall on deaf ears did she speak her heartfelt thoughts.

"You don't need to keep purposely pushing people out of your life, you know? I have no idea why you are always insistent on doing everything alone but there will always be people who are willing to help you if you so much as stop and turn around, Haruto-kun."

He paused in his tracks. His face is one of calmness but his eyes betrayed his emotions.

Rage, sorrow, determination, protectiveness.

"Shut. Up."

He left her behind with those two words and he walked on ahead, fuming in silent fury. Guess her words had hit where it hurts him the most. Haruto had always been polite, saying something like that is not like him. She must have pushed too far.

Still, she ran after him. She became a Demon Slayer to protect others and their smiles. If she couldn't even make a single person smile then she would have failed. He's her pillar of inspiration, the person who made her dare to dream to become a Hashira. She will make him smile again. She will start from being his friend.

That's the least she could do.

"Where are we going?"

"A detour back to my home."

She shamelessly walked behind him the entire time. He didn't make an effort to shake her off but he didn't bother to turn around to ensure that she could keep up with him either. He simply walks at his own pace.

She saw how he patrolled and purposely made an effort to sniff out the demons hiding in the area, quite literally. His keen sense of smell is really something to behold. There's a certain area which he combed through a lot more thoroughly than most. Now that she knows that is where his family is staying at, it made sense.

He began to climb up a mountain and she quickly followed, not wanting to get lost within the woods. The way he travelled through it with practiced ease made her certain that right on this mountain is where he used to live.

She soon saw it, a straw hut.

"HARUTO ONII-CHAN!"

A bunch of children ran up to greet him with a big hug the moment they spotted him, toppling him over his feet. Haruto laughed as he ruffled their hair and hugged them in return. It's the first time she saw it, the first time she saw him laugh from the bottom of his heart.

"Have you been behaving when I'm not around?"

"We did!"

"Onii-chan? Who is this pretty onee-san?"

"Look, she also has a sword like onii-chan!"

"Wow! Do you think she can dance the Dance of the Fire God too?"

"What did I used to tell you when you guys are greeting somebody else?" Haruto adopted a slightly sterner tone, the tone an older sibling would use when reprimanding their younger sibling. She would know. She uses it on Shinobu too when she gets out of hand.

Haruto's younger siblings immediately straightened themselves and began to greet her.

"Uh, it's nice to meet you, onee-san! I'm Nezuko!"

"Hanako!"

"Takeo! That is Shigeru and he is Rokuta!"

"It's nice to meet you, I'm Kocho Kanae." Kanae greeted the children with a smile. "I never knew Haruto-kun had siblings."

"Wha? Onii-chan! How could you not tell her about us?!"

"She didn't ask. And stop shouting, Takeo, my ears are starting to hurt. And where's father and mother? Tanjiro? Where is he?"

"They are in town to sell firewood! Father is showing him the ropes! Mother left me to take care of everyone!"

"Thank you, Nezuko. You did a great job." Haruto patted Nezuko on the head fondly. "Is father feeling better?"

"Uh, no?" Nezuko looked a little down at that. "We tried to buy the best medicine we can afford but father always says to not spend the money on him and save it for future use instead. Even mother could not convince him otherwise."

"I see. I will try and talk some sense into him then."

"Please do, onii-chan! Father keeps coughing non-stop nowadays! Tanjiro nii-chan wanted to just go to town alone but father insisted on keeping him company! He is in no condition to move around! Mother is worried about him so she accompanied him as well!"

Haruto simply sighed at those words.

"You guys haven't started to prepare dinner, right? How about we make dinner together while waiting for them to come back?"

"Yay!"

"Then will you dance the Dance of the Fire God after that? Please! Please!"

"Sure."

"Yay!"

She never knew Haruto is capable of giving such a gentle look, she didn't know that he could smile so lovingly until then. It was right then that she knew the reason why he became a Demon Slayer. There could be no other reason.

He wants to protect his family from demons.

"You should eat more! Look at you, too skinny! Oh dear, why didn't Haruto say anything about bringing a lady friend over?! We would have prepared better food if that was the case! This is the first time Haruto ever brought anyone home! Haruto! Next time, at least send a letter over first if you are bringing anybody home to visit us! Especially if it is a lady!"

"I didn't ask her to come. In fact, I told her to leave. She just followed me up here."

"Haruto!"

"It's alright, Kie obaa-san. It's true that I followed after Haruto-kun without permission. I shouldn't have stayed and impos-"

"None of that! This is Haruto's fault for not being a good host!"

"I'm glad that you came up here with him." Tanjuro said with a laugh. "Feel free to visit us whenever you like, Kanae-chan. A friend of Haruto is a friend of ours as well."

"Hey onee-san! Are you a beast hunter like onii-chan as well?"

"Beast… Hunter?" Kanae asked, feeling a little confused.

"Yes, she is." Haruto quickly answered on her behalf when Tanjiro asked her that question. "Eat your food before it gets cold, Tanjiro."

She gave Haruto a look which he pointedly ignored. Guess someone is not all that forthcoming about his real job.

"This money should last you for more than two months."

It's after dinner. She had volunteered to wash the dishes but the Kamado siblings practically kicked her out of the kitchen, saying that she's their guest and shouldn't need to do such a thing and should instead spend more time with their onii-chan.

She's starting to think that the children are getting the wrong idea about her relationship with Haruto.

She walked back out of the kitchen only to be greeted with the sight of Haruto passing money to their parents. She stayed out of sight and hid herself behind a wall, not wanting to interrupt the Kamados.

"Haruto, this is too much! We don't need to spend that much!"

"Take it. And father, why are you not taking your medicine? Your health isn't getting any better."

"I know my body better than anyone, Haruto. I'm probably not going to last for much longer, medicine or not." Tanjuro said with a peaceful smile on his face and ruffled Haruto's hair fondly. "I'm glad I get to see you one last time before I go. You've grown to be a fine man. I'm proud of you."

"Father, please don't say something like that. You will live, okay? Just take your medicine. Please."

"At least I get to see my future daughter-in-law before I go." Tanjuro acted oblivious to Haruto's words as he laughed goodnaturedly. "Kanae's a good girl, Haruto. Treat her well."

"I barely know her. She's just a colleague from work." Kanae heard Haruto giving an exasperated sigh before she heard him opening the cloth bag he was carrying around. "This is the new batch of wisteria incense and the small bags of wisteria flowers I packed for the kids. They are carrying those around with them all the time, right?"

"We made sure they do. They still think it is a good luck charm. Don't worry, we made sure to light the incense every night."

So Haruto is protecting his family from demons in his own way. Haruto's siblings may not be privy to what he really does for a living, but it seems that his parents are in the know.

"Kanae-chan, there's no need to feel out of place here. Come join us."

Tanjuro's voice got her to snap her head back up in alarm. How did he notice her presence? She is hiding herself behind a wall, her presence is concealed thanks to her breathing techniques. It's not possible for any ordinary human to detect her presence.

Reluctantly, she showed herself. She bowed awkwardly, not knowing how she should react when she was caught eavesdropping in this manner.

"Sorry for intruding. I didn't mean to listen in."

"It's not like what we are talking about is a secret." Tanjuro said with a gentle smile, his warm eyes seemingly able to see through her. "To be a Demon Slayer at this age, life must be hard for you too. Even then, I have a favour to ask. Help us to take care of Haruto in our stead, alright?"

"Father. I do not need-"

"Okay!" She chirped back happily, partly just to annoy Haruto and partly because she wants to take care of him as a friend.

"Haruto may be one of the strongest Demon Slayers in the Corps but I swear, he rarely smiles! The number of times he did could be counted on a single hand! The only friend he has is Rengoku-san! I will get him to smile more and make more friends, I promise!"

"Kanae."

"Really?! Haruto! We didn't raise you to be so antisocial!"

"Mother, I-"

"You need to make more friends!"

"You know what? I give up." Haruto surrendered with a sigh. It's at this moment when Haruto's siblings came barreling into the room.

"Onii-chan! We finished washing the dishes! Come on, dance the Dance of the Fire God for us! Oh, oh, maybe this onee-san can dance with you too!"

"She doesn't know the Dance of the Fire God." Haruto replied patiently to Takeo's endless barrage of words as he stood up and picked up his sword. "Come, let's go outside."

Kanae doesn't really know what is going on, but she had heard about Haruto figuring a Breath Style all on his own through a dance that was passed down in his family for generations. This might be it.

"Look carefully, Kanae-chan. There's a lot you can learn from the Dance of the Fire God." Tanjuro spoke with a smile as she sat with the Kamado family on their front porch, watching Haruto standing alone in the huge clearing. She smiled back at the man, still not knowing what he meant.

She watched as Haruto slowly got into a stance and in slow motion, began to draw his sword out from its sheath. She watched as he slowly went through the motions form by form before it got faster and faster and when he repeated the entire cycle, her eyes widened.

Isn't what he is currently using the Breath of Fire and their respective Forms? She had seen it enough times during her spar with Haruto. It's the exact same thing.

"That's the first segment, Dance."

Kanae can only listen on in confusion and awe as she watched Haruto performing the Dance of the Fire God while Tanjuro patiently explained the name of each segment, twelve in total, meant to perform in repetition from sunset to sunrise.

That's… this is a Breath Style, no doubt about it. Now that she has the time to see it up close and perform in slow motion, she can see it. The Dance of the Fire God is a Breath Style, one unlike anything she had seen before. It's even more complicated than any other form of Breath Style that she knew of.

"Haruto started learning it when he was four. Kept bugging his father to learn it even. He would never stop practicing the dance in his free time, saying that it is his responsibility as the eldest to learn it and perform the ceremony so that Tanjuro would not need to do it because of his ailing health. He would come back every new year without fail to perform the ceremony for us."

Kanae nodded at the words, her mind still trying to piece out the mystery. If the Dance of the Fire God is indeed a Breath Style passed on within the Kamado family for generations, it would explain certain things. Like how Tanjuro noticed her presence when she was actively trying to conceal it. Like how Haruto was able to easily slay a demon without any prior training and achieved Total Concentration Breathing all on his own without a teacher.

He's not a genius, not truly. He had put in a lot of hard work to master his Breath Style through endless repetition of this Dance of the Fire God. For eleven years he had been practicing this dance over and over again. First, as a ritual ceremony as the eldest son of the Kamado family, then as a Demon Slayer said to practice the Breath of Fire. The Breath of Fire is simply the Dance of the Fire God. No more, no less.

The more she thinks about it, the more she is convinced that somewhere long ago, the Kamado family must have been involved with the Corps. There is no other explanation for the existence of this unknown Breath Style.

She watched on with the Kamado family, mesmerised by the way he danced with his sword under the silver moonlight.

"The both of you cannot stay for the night?"

"We are on a mission, mother." Haruto patiently explained. The Kasugai crows had arrived with a new mission when Haruto was halfway with his dance. Haruto had stopped his dance immediately and she had also stood up in response, ready to slay demons.

"Onii-chan, do you really have to go again?"

"I'm sorry, Tanjiro, but I have to go." Haruto patted Tanjiro on the head. "Did you see the dance clearly this time?"

"I did! I'm only able to complete three segments without stopping as of now, but I will be better when you return the next time! I promise!"

"I'm sure you can do it." Haruto said those words with the gentlest smile Kanae had ever seen. "And when that day comes, we can perform the ceremony together."

"I want to do it too!"

"Me too!"

Haruto's younger brothers began to make a ruckus and Kanae cannot help but let out a smile at the sight. She can understand now, the childish innocence of his siblings that Haruto is so desperately trying to protect.

"Take care of yourselves, father, mother. I will be going now."

"Take care, Haruto. You too, Kanae."

With that, they left. They were halfway through descending the mountain when she asked.

"The Dance of the Fire God is a Breath Style. Were your family Demon Slayers?"

"No."

"But-"

"Breath Style is not something only entitled to Demon Slayers. Our family has been charcoal burners for generations, I've checked our family tree."

"I… see."

"I don't think I need to remind you, but don't tell a single soul about the truth of my Breath of Fire. I don't want my family to be involved with the Corps or anything demon related in general."

"I understand."

"You better."

"Do you have so little confidence in me?" She pouted in mock anger. "I can keep a secret! I'd thought we were friends! Even your parents told you to be friends with me!"

"That's their own delusion. I didn't join the Corps to make friends. Protecting my family from demons is the only reason why I'm here, you do well to remember that."

He took off with a greater dash of speed and she hurriedly followed. Somehow, she cannot help but feel that there's a greater underlying fear that drives Haruto forward in becoming a Demon Slayer. Why is he so sure that he has to be a Demon Slayer to protect his family? He has been practicing the Dance of the Fire God since he was four. If he has the Dance of the Fire God at his disposal he is more than enough to dispatch any ordinary demon that might wander close to his home. He doesn't need to become Shinjuro's Tsuguko and get himself inducted into the Corps. Demons of the Twelve Demon Moons would not possibly wander into the remote location where his home is in the mountains. Haruto has no need to be a Demon Slayer to protect his family.

So, why? What is it?

What is Haruto's real reason for becoming a Demon Slayer?

"There's no demon here. Are you sure this is the correct place?"

Kanae watched on as Haruto was so very close to strangling his Kasugai crow for making them run around in circles.

"It's here! Our information network said so!"

"Well, then the information network is clearly wrong!" Haruto seethed. "Who knows where the demon may be now?!"

"Maybe we should wait for further-"

"No. A second wasted here is a second more dangerous for the demon's next victim. We are tracking the demon down manually, screw whatever the information network says." Haruto cuts her off before she can get her point across. There's logic to his words and she knows Haruto is more than capable of tracking down demons using only his nose.

Thus, they continued their trek as they kept running to wherever Haruto's nose pointed them to. It took them a few days but it didn't take them long to realise that they are going back into the direction which they first came from.

The area where Haruto's home is.

"Fuck! Fuck fuck fuck!"

She heard him swearing up a storm as he picked up his pace and she followed close behind. They have been travelling non-stop without rest for two whole days. They are getting closer and closer to the area where his house is, the same direction the demon is heading to.

She knows how important his family is to him. Protecting them is the reason why he became a Demon Slayer in the first place.

"Haruto! I'll go check the town! You go check on your family!"

"Thanks." He replied without looking back and faded out of view. The next thing she knew, he's already ahead and heading for the mountain where his family is. She took a left and headed for the town at the bottom of the mountain. The chances of the demon appearing within the town is much higher because there are more people here for the demon to feast on, so she must be on alert.

She will not let a demon claim another victim if she can help it. Not on her watch.

"Father! Father!"

She couldn't believe her eyes either. Why? Why did the demon appear in the mountain where Haruto's family is?

Once she had quickly made her rounds and was extremely sure that the demon couldn't be hiding in the town, she headed up for the mountain to meet with Haruto. It was past midnight by then. The only sight that greeted her was a large amount of blood splattered around the front of the Kamado's house and Haruto kneeling over his father's body together with the rest of his family.

No way. Why? Why were they still too late? Tanjuro was still eating and laughing with them just a few days before.

Why is it the kind people who always die first?

"You all are coming with me, mother. I am not going to accept any objections."

"But Haruto! This is our ancestral home!"

"And our home is no longer safe." Haruto bit out harshly. "If it wasn't for father holding out long enough for me to arrive, all of you would have died to that demon. I cannot protect you forever, not when I just found out that there are now demons who can temporarily withstand the effects of wisteria incense lurking about in this area. That demon just now was on par with the Lower Moons of the Twelve Demon Moons, the twelve strongest demons in existence under Muzan's command. We are moving."

Kanae can only watch as Haruto continues to have a heated argument with his mother. She and Haruto's siblings can only watch from the side.

"Kanae-san? W-Was what k-killed father… really a demon?"

"Yes." She replied to Tanjiro's question honestly. "Your brother and I, we are Demon Slayers. We slay demons. Sorry. I'm sorry for not getting here fast enough to be of help. We were tracking the demon down only to track it back here. This shouldn't have happened, I'm sorry."

"I-It's the demon who needs to be sorry!" Nezuko cried out as tears fell freely down her face. "F-Father, h-he-!"

The only thing Kanae can do is to hug Haruto's siblings close. They are so very lucky to be alive. If it wasn't for Tanjuro who kept the demon busy long enough for Haruto to show up, the entire Kamado family would have been massacred. Tanjuro doesn't have a Nichirin Blade so he could not kill the demon. It doesn't help that his body is already very frail to begin with due to his illness. He passed away in Haruto's arms not long after Haruto arrived.

Upon Haruto's insistence, the entire Kamado family packed up and left the mountain the next morning after they had laid Tanjuro to rest. In Haruto's hands are the hanafuda earrings Tanjuro passed to him before he passed away.

"Tanjiro, here. You keep these."

"B-But onii-chan! These are-! Father left these for you!"

"And I'm not going to be the one who will succeed them, not with what I'm currently doing. You take these, it's final."

Throughout the entire journey, Haruto didn't talk much. Kanae knows that he must be feeling a lot of grief, sorrow, regret, and guilt for not being there in time to save his father, but there's really nothing she can do for him at this moment. Haruto's family are equally distraught at Tanjuro's death, but it is also obvious that they are worried about Haruto's mental state.

Yet, there's nothing which they can really do.