As he gazed upon the scene in front of him, Giyuu was struck by a sense of uncertainty that he hadn't felt since he was a child.

Shinobu was smiling at Tanjirou, her blade held at the ready. Meanwhile, Giyuu could see Tanjirou biting his lip nervously, clearly hesitating on what to do.

Giyuu still couldn't believe they were here. The two demons he had spared on that fateful day. He had returned to the snowy mountain where he first met them more than once, but every time, the old man had stopped him from seeing them, promising him that they were being taken care of.

He still remembered just how extraordinary they were. The demon girl who protected the boy without a second thought, blocking an attack aimed at him with her own body. The demon boy whose eyes had been so kind and warm, eyes that had reminded him of Sabito.

And now they were here, on a mountain surrounded by demon slayers. Facing against two Pillars to boot.

Emotions warred agitatedly within him even as his expression remained impassive.

What should he do? Should he help Shinobu? But he didn't want these two demons to die. Yet at the same time, if he betrayed the Demon Slayer Corps and aided these two demons...

"Please let us leave?" Tanjirou asked, a pleading note entering his voice.

"Nope!" Shinobu replied cheerfully.

Giyuu saw the moment Tanjirou realized that he would have no choice but to fight.

He saw the determination appear in the demon's eyes as he steeled himself.

And, most importantly, he saw how Tanjirou had shifted his body so that he was standing in front of Nezuko, shielding her from them.

A boy who wanted nothing but to protect his sister...

At that moment, Tomioka Giyuu made up his mind.

XxX

"Nezuko," Tanjirou said quietly. "When I say run, run. I'll hold them back." Nezuko looked at him, the only sign of emotion being the faint flickering of her pink eyes.

"Oh?" Shinobu smiled. "You're trying to save your sister? How noble of you."

Tanjirou didn't respond, instead gripping his sword tightly.

There was another moment of tense silence.

To Shinobu's surprise, it was Giyuu who broke it.

"Kamado Tanjirou," the Water Pillar spoke, his tone betraying no emotion. He regarded Tanjirou with dull blue eyes. "Go."

Before Shinobu could comprehend what he meant, Tanjirou abruptly exploded into motion. Shinobu tensed up but blinked when Tanjirou merely bowed down.

"Please forgive me!" he yelled, somehow sounding genuinely apologetic. "Thank you, Tomioka!"

Then Tanjirou promptly sheathed his blade, spun around, crouched down to let Nezuko climb onto his back, then ran away without looking back.

Shinobu blinked again, her expression disbelieving. Just for a second though. She regained her composure a moment later, her muscles coiling as she prepared to hunt them down -

When Giyuu grabbed her arm in a vice grip.

A beat.

"Tomioka?" Shinobu said sweetly. "Unhand me so I may capture those two, please."

"I cannot."

"I don't understand. Are you going to let those two demons get away?" Shinobu's smile didn't waver, but something dark appeared in her purple eyes.

"Yes," came the short reply.

Shinobu hummed. "You do know that you're breaking the Demon Slayer Corp rules, aren't you?"

There was a short pause. Then, "I know."

"Very well then," Shinobu nodded. Kanao watched on calmly as the two Pillars remained in their positions for a second.

Then Shinobu moved, whirling around and thrusting her palm into Giyuu's stomach. He grunted as he was forced to let go, and she jumped back to gain some distance. Simultaneously, Kanao exploded into action, taking advantage of the opening to sprint on ahead after the demons with only a broken sword.

Shinobu's smile finally left her face when Giyuu drew his sword and entered a stance.

"You would raise your blade against me?" she asked, and despite her lighthearted tone, she couldn't quite mask the sudden hurt in her voice. Imperceptible to most people, but not him. A pang of guilt shot through him. However...

Giyuu raised his blade, his message clear.

You shall not pass.

"I see," Shinobu smiled at Giyuu. It was a terrifying smile. "Then I'll just have to go through you."

XxX

Tanjirou ran, pushing his demonic body to its very limit, the forest around him but a blur. On his back, Nezuko shifted around to get into a more comfortable position.

Behind him, he could hear the sound of combat - Giyuu was fighting Shinobu so they could escape. Tanjirou needed to thank him later. For now, however, he had to focus on getting away.

Unfortunately, Tanjirou smelled one pursuer chasing after them. It was the girl he had saved - Kanao. Somehow, she was easily keeping up with his pace.

They made it to the base of Mount Natagumo. Thankfully, there was another mountain off in the distance - they could stay the day there. But...

He glanced up at the moon worriedly. Would he have enough time? Dawn was approaching.

Damn it. He had no choice; with demon slayers now swarming the mountain, he couldn't double back lest he risk fighting them. There should be enough time until the sun rises. He began sprinting again, praying that he hadn't miscalculated and doomed Nezuko and himself to a fiery death.

And Kanao was still right on their tracks. He needed to lose her.

After about ten minutes of nonstop running, they arrived at the base of the smaller mountain with the moon still thankfully shining safely in the sky. He quickly located a cave for them to stay in for the day.

That was about the time when Kanao finally caught up to them.

Tanjirou whirled around as she materialized in the clearing, an empty smile on her face. She had only a broken sword with her. Tanjirou eyed it incredulously. She couldn't possibly be planning on fighting him with that?

Apparently, she was planning on doing exactly that because she readied her blade. She didn't say anything though, instead smiling at him.

As the silence grew, Tanjirou only grew more and more uncomfortable. "Umm, I don't want to fight you. Could we - "

He was cut off when Kanao blurred. He hastily drew his blade to block her attack. They exchanged blows, Tanjirou fending off her relentless attacks. Oddly enough, however, her heart didn't seem to be in the strikes; there was no real intensity behind them, as if she was merely going through the motions as a formality. It felt more like a spar than a real fight -

Tanjirou's eyes widened as the first rays of dawn streaked across the landscape.

The sun was rising.

Panic shot through him before he breathed.

Breath of the Sun, Fourth Form. Fake Rainbow.

His footwork pattern changed as he began utilizing high-speed twists and rotations to leave behind afterimages. Kanao's eyes darted around, trying to track him with her extraordinary eyesight. However, the afterimages oscillated and shifted in and out of focus, throwing her off.

For a brief moment, worry flashed through her.

What if she was wrong about him? Was she about to die?

Then there was a sharp pain in the back of her neck. An effective, but nonlethal strike.

Ah, she thought as her vision went dark. So I was right, after all.

XxX

Tanjirou quickly caught Kanao as she collapsed, having fallen unconscious from the edge-hand chop to the nape of her neck. Guilt shot through him but he suppressed it. Daylight was coming. He had no choice.

"Get into the cave! Hurry!" he shouted to Nezuko. She made a noise of assent, swiftly entering the cave.

Tanjirou then glanced at Kanao. For a second, he considered just leaving her lying in the middle of the forest, but he quickly dismissed that idea. His mother would never forgive him if he treated a lady like that. Besides, it would be a scummy move.

But what should he do-?

He winced as his skin began steaming.

There was no time to waste.

He made his decision in a split second, rushing into the cave as the sun slowly rose overhead, Kanao still in his arms.

XxX

Nezuko looked at him.

Then she looked at Kanao, who was lying on the ground, Tanjirou's rolled-up haori serving as a makeshift pillow.

Then she looked back at him.

"I didn't want to leave her unconscious in the middle of the forest," Tanjirou explained.

Nezuko gave a quiet hum of understanding before curling up beside him. He absently stroked her hair, leaning back against the wall of the cave from where he was sitting.

"We did it, Nezuko," he whispered, a smile spreading across his face. "We defeated a Demon Moon. Now we're one step closer to turning you back into a human."

All Tanjirou heard in response was soft, even breathing. Nezuko had already fallen asleep.

He laughed quietly.

"Good night, Nezuko."

XxX

Kanao woke with a start, her eyes snapping open. She was lying on a hard, uneven surface. There was something soft under her head.

Everything came rushing back to her. She had followed the demon - Tanjirou - to a cave, where he had knocked her unconscious when the sun rose. After that, what happened?

Kanao sat up, observing her surroundings. She was in a dim cave, the only source of light coming from the entrance a solid five meters away. Glancing down, she saw that her head had been resting on a rolled-up black-and-green checkered haori. Her sword was nowhere to be seen.

"You're awake."

Kanao snapped her head around to see Tanjirou sitting against the wall of the cave. Nezuko was snuggled against him, fast asleep.

"I'm sorry about earlier," Tanjirou continued, scratching his cheek awkwardly. "But... well, the sun was coming up, so I panicked and knocked you out. I hope you're alright."

Kanao smiled, her pink-lilac eyes emotionless.

After waiting several seconds for her to respond, Tanjirou coughed awkwardly before smiling back, and Kanao was once again taken aback by the sheer kindness and care in his smile. "If I may ask, why did you attack us?"

Kanao continued smiling.

"You weren't fighting for real earlier, weren't you?" Tanjirou pressed. "I could tell by the intensity of your attacks. Why did you hold back?"

Kanao regarded him for a moment with the same empty smile. Then, she reached into her haori and withdrew a single well-worn coin.

"Oh, what's that?" Tanjirou asked enthusiastically, his eyes lighting up with curiosity.

She didn't respond, instead flipping the coin into the air.

Tails, I speak. Heads, I don't.

It landed heads.

Something rose up deep within her. It felt similar to the anger she had felt when facing Rui, although of a much lesser degree. Annoyance or irritation, perhaps? She didn't know. Whatever it was, she didn't like the feeling of it. It was unpleasant.

However, the coin had landed heads. And so, she wouldn't speak.

She looked back at Tanjirou and smiled.

Slowly, Tanjirou's smile dimmed as he realized that she wasn't going to respond. "Oh," he said, seeming crestfallen. "I-I'm sorry. I just remembered that I'm a demon and you're - well, a demon slayer."

No, it wasn't that. It was just because she couldn't make choices of her own, so her coin made it for her. It had nothing to do with the fact that he was a demon.

"I'll stop bothering you," Tanjirou said, his smile becoming sad. "You may leave if you want. I won't keep you here. Just... please, I beg of you, don't bring back the demon slayers." The sun was still out, meaning that he couldn't escape.

She wouldn't do that. He had saved her, after all. It may be against the Corps rules, but...

I truly believe that someday, there will be a demon who has never harmed a human. And if I ever meet such a demon, I will gladly give them my cherished love until I die, for demons are tragic, hopeless creatures. Peace will come one day, Kanao, and when it does, we must be prepared to accept it with open arms.

When given the option between following Corps rules or fulfilling Kanae's dream... The choice was clear.

So there was no reason for his smile to look so sad. No reason at all.

Tanjirou let out a heavy sigh. "You may not believe me," he said, his tone dejected, "but I was telling the truth when I said that we had never hurt a human before. I swear."

She knew that he had been telling the truth. Her supernatural eyesight had confirmed that - his body language and expression had been entirely sincere. Sure, at first she hadn't fully believed it, but after he had used non-lethal measures and she woke up unharmed, she knew that he was being genuine.

So why... why was his smile disappearing?

"But... I'm a demon now," Tanjirou's gaze was downcast, and Kanao felt a pang of something shoot through her when she saw his smile completely disappear. She... She didn't like this feeling. "I understand why you wouldn't trust me - "

"I believe you."

The words escaped her before she realized it.

Tanjirou glanced upward sharply, hope suddenly entering his eyes. "You do?!"

Kanao nodded, still not believing that she had spoken. "I have good eyesight. I know you weren't lying."

Tanjirou beamed at her, exuding pure relief and happiness, and the unpleasant feeling within Kanao instantly vanished. "I'm glad!" Then he tilted his head. "Wait, so why did you attack us earlier?"

"... orders."

"Oh," Tanjirou paused before asking, "Did you want to attack us?"

Kanao was silent.

Tanjirou smiled. "I see. Thank you."

Kanao didn't respond, but her smile did seem slightly more natural. She stood up. "I need to go now," she said softly.

Tanjirou nodded. "Alright. Stay safe. It was nice meeting you!"

Kanao inclined her head before making her way out of the cave. At the entrance, she paused for a moment, turning back slightly to look at him.

"Once I catch up to my comrades, the sun will have already set. You'll have more than enough time to escape."

Tanjirou's eyes widened before his smile widened. "Thank you," he said. "Bye Kanao!"

Several foreign emotions flickered across her eyes.

"Farewell."

With that, she exited the cave and began returning home.

It wasn't until she was leaping from tree to tree to get back to the Butterfly Estate when a realization hit her.

Kanao had just disobeyed the coin.

But strangely enough? She was perfectly fine with that.

XxX

True enough, Kanao kept her word. By the time night fell, not a single demon slayer had come, to Tanjirou's immense relief. Then he felt guilt for doubting her.

Even though they had killed Rui, there were still more Demon Moons to hunt. As such, Tanjirou and Nezuko prepared to start roaming again.

XxX

Unfortunately, for the next few weeks, luck was not on their side. Aside from a few demons that Tanjirou dispatched with ease, they didn't meet any of the Demon Moons whatsoever.

Then, three weeks after the events on Mount Natagumo, they finally found someone.

They didn't meet a Demon Moon, though.

Instead, they met Kibutsuji Muzan himself.

Needless to say, things did not go well.

XxX

It had all started with a smell.

They had just arrived at a city and were asking the local populace if there was anything suspicious happening recently, any missing persons, and so on, when a familiar scent entered Tanjirou's nose.

He immediately froze up in shock before his breathing became shallow and irregular, nearly hyperventilating.

Tanjirou knew that smell. He would never forget that smell as long as he lived. The smell of that man.

Nezuko looked at him curiously.

"H-He's here," Tanjirou whispered, his hands shaking. "Kibutsuji Muzan."

A growl escaped Nezuko as veins bulged on her face, her pupil dilating into slits. Tanjirou probably looked the same, judging by the wary looks the passing-by pedestrians were giving them. He didn't care.

They broke into a sprint, Tanjirou tracking the scent. Adrenaline pumped through his body and his heart was hammering so hard it felt like it would break out of his chest.

After several turns and corners, the two siblings found themselves in a dark, secluded alleyway. Standing in it was a man with unnaturally pale skin. He wore an embroidered black tuxedo and had on a white fedora with a red ribbon. And that face... The cruel red eyes that had haunted many of Tanjirou's nightmares...

There was no doubt about it. This was Kibutsuji Muzan.

Tanjirou's vision became tunneled as he stared at Kibutsuji, his internal temperature rising rapidly.

Kibutsuji didn't appear to have noticed them yet. He was currently holding up a human by the throat, and Tanjirou realized with a start that Kibutsuji's fingers were digging into the man's throat.

Before Tanjirou could say anything, the man began screaming, thrashing around in pain before stilling. Kibutsuji dropped him and the man landed in a heap on the ground. Dead. Tanjirou's heart squeezed painfully as the anger within him grew.

Beside him, Nezuko growled, her claws lengthening. The sound drew Kibutsuji's attention. He turned toward them, his eyes narrowing.

"Oh? Two demons?" he spoke, a hint of confusion creeping into his deep voice. "Why didn't I sense you...?"

"Kibutsuji Muzan," Tanjirou growled.

Kibutsuji's eyes flashed when Tanjirou said his name. "You dare?" he seethed before freezing when he caught sight of Tanjirou's hanafuda earrings. Recognition entered his gaze. "You're that kid." His gaze shifted over to Nezuko. "And you... You two were his descendants - "

Tanjirou breathed, the heat that had been building up within him detonating. The scar on Tanjirou's head darkened - the Demon Slayer Mark. Tanjirou had awakened it after a particularly brutal training session with Yoriichi.

Simultaneously, a strange calm settled over him as the world became slower - or rather, his perception of the world became many times faster. He had only ever entered this state twice before, once when he had fought Giyuu all those years ago on that snowy mountain and once when he had fought Yoriichi during the final test.

Transparent World.

Kibutsuji's form flickered before Tanjirou saw his muscles and bones and blood flow and - was that seven hearts and five brains?!

No matter. Tanjirou just had to destroy them all then.

Breath of the Sun, Seventh Form. Sunflower Lance.

Flames erupted along the edge of his sword as he blurred forward, crossing the distance in a blink of the eye. Kibutsuji's eyes widened in shock as Tanjirou's sword pierced through one of his hearts, blood splattering outward. "What-?! That blade," he breathed disbelievingly, looking down at the black Nichirin blade. "It's his."

His blade still implanted in Kibutsuji's chest, Tanjirou slashed outward, tearing through flesh with ease. Kibutsuji coughed out blood. Continuing the slash, he rotated in place, spinning around and redirecting the momentum of his blade to cut into Kibutsuji's neck.

Flesh burst out of Kibutsuji's side, a massive appendage twice the size of Tanjirou's body that blocked his strike. At the same time, barbed whips exploded out Kibutsuji's midsection, streaking towards Tanjirou.

Breath of the Sun, Second Form. Clear Blue Sky.

Tanjirou spun vertically, slicing in a circular arc perpendicular to the ground that severed all the whips. He landed in a low crouch before spiraling into the air.

Breath of the Sun, Tenth Form. Beneficent Radiance.

Flames whirled around them in a raging inferno as Tanjirou unleashed a powerful slash that was blocked by even more flesh that surged outward.

Suddenly, Tanjirou saw with his Transparent World that Kibutsuji's torso and upper body morphed into a gigantic beastly mouth. He barely had enough time to brace himself before a piercing scream slammed into him, the force of the shockwave damaging several of his internal organs and causing his entire body to lock up.

Tanjirou coughed out blood as he struggled to regain his bearings. Fortunately, instead of taking advantage of the opening, Kibutsuji turned around and fled with astounding speed, disappearing into the darkness.

Was - was he running away?

"Come back, you coward!" Tanjirou screamed. Kibutsuji cast a murderous glance over his shoulder before snapping his fingers.

Two demons materialized in front of Tanjirou - a girl holding temari balls and a man with closed eyes. They blocked Tanjirou's path. The girl smirked and began to say something.

Breath of the Sun, Fifth Form. Fire Chariot.

Tanjirou didn't even spare them a glance, leaping into the air and cutting them all down in a single burning strike. Their heads dropped to the ground and their bodies began disintegrating as Tanjirou rushed past them, chasing after Kibutsuji.

He burst out of the alleyway - and he drew in a horror-filled breath.

People were turning into demons on the street, small wounds on their necks. He saw Kibutsuji running away, disappearing into the crowd of panicking people.

Tanjirou gritted his teeth. If he got distracted now, then Kibutsuji would get away. However, it wasn't like he could leave these people either.

Damn it. Damn it. Damn it!

"KIBUTSUJI MUZAN!" Tanjirou roared. "I WON'T LET YOU GET AWAY! NO MATTER WHERE YOU GO!"

Demons fell to the ground as Tanjirou dashed around the street, a veritable inferno of flames surrounding him.

"YOU WON'T EVER GET AWAY FROM ME! I'LL FOLLOW YOU TO THE DEPTHS OF HELL ITSELF, AND MY BLADE WILL CLAIM YOUR HEAD!"

He was just a blur of movement by this point, but even as he cut down the horde of demons, his eyes were solely focused on Kibutsuji's retreating form. The Demon King was almost out of sight now. Anger coursed through Tanjirou's veins.

"FOR AS LONG AS I BREATHE, I WON'T EVER FORGIVE YOU!"

With that, the final demon fell. Tanjirou breathed heavily, his Demon Slayer Mark and Transparent World disappearing. He briefly contemplated following Kibutsuji's scent, but that would only result in more people being forcibly turned into demons. He couldn't allow that.

Thank the gods nobody else had been hurt; he'd managed to protect all the humans from the rampaging demons. But as for the demons themselves...

"Damn it," he whispered one last time, clenching his fists so hard his claws drew blood. A tear slowly trickled down his cheek, of sadness and rage and frustration and bitterness.

Nezuko ran up next to him. She took one look at him before reaching out and hugging him tightly. Tanjirou buried his face into her hair, his entire body shaking like a leaf. He stayed like that for several moments.

Finally, he pulled away, wiping furiously at his eyes.

"Let's go. We need to leave before the police come."

Nezuko gave a hum of understanding. Together, they ran away, leaving behind nothing but piles of ash.

XxX

Fear.

Pure, unadulterated fear coursed through Kibutsuji Muzan's body. His entire body trembled and his pupils dilated in and out.

What the hell was that? What in the utter hell was that?

Even though he was a demon, the boy was able to resist Kibutsuji's control and even break free of his curse.

And, more importantly...

Just like that man, the boy knew the Breath of the Sun. Just like that man, he had a mark on his forehead. Just like that man, he had no battle presence whatsoever. And those hanafuda earrings and that black Nichirin blade... Those were the exact same.

The memory of Yoriichi Tsugikuni looming over him flashed through his mind, sending a fresh wave of primal terror cascading throughout his body.

Kibutsuji took several deep breaths. Slowly, he calmed down, rational thought returning. The boy was weak. Compared to that man, it wasn't even a contest. Kibutsuji could've easily defeated him if the irrational fear hadn't consumed his mind. The boy wasn't a threat to him. Not at all.

However...

That boy still irritated the living hell out of him.

He made his next decision instantly without a hint of hesitation.

For the first time in centuries, Kibutsuji Muzan summoned the six Upper Demon Moons.

XxX

He hadn't been strong enough.

Fundamentally, he knew that it made sense. Kibutsuji was literally centuries old with far more battle experience than him. He had evaded the Demon Slayer Corps since it had been founded and had slaughtered countless skilled demon slayers. He wasn't the Demon King for nothing.

And yet...

It still hurt.

Knowing that he was too weak, knowing that he wasn't able to avenge his family, knowing that the only reason he hadn't died was because Kibutsuji was apparently a coward...

Tanjirou took a deep, calming breath, counted to ten, then released it.

Well, there was no point in wallowing in self-pity. He needed to work hard, harder than he had ever worked before.

If the gap between him and Kibutsuji was immeasurably wide...

Then he would just have to close it.

Drawing his blade, he prepared to train once more.

A sound drew his attention. He turned around to see Nezuko there.

"Huh? What is it, Nezuko?"

Nezuko's claws sharpened and veins pulsed to life on her face.

Tanjirou frowned momentarily in confusion before understanding dawned. "You want to train too?" he asked.

Nezuko made a noise of agreement, her typically impassive eyes aflame with determination.

And Tanjirou remembered. He wasn't the only one who had suffered at the hands of Kibutsuji Muzan. Nezuko had been there too, and she was probably just as furious as him, if not even more so.

"You're right. I'm sorry. During that battle, I completely forgot about you - I just rushed at Kibutsuji Muzan without thinking."

Tanjirou smiled, an identical look of determination appearing in his eyes.

"Next time, we'll defeat him together."

XxX

And so they trained. They stopped roaming around - it was unlikely for them to just randomly run into a Demon Moon anyway.

Until one night, the cat Chachamaru appeared in front of them, a letter on its back.

Tanjirou brightened at the sight. Tamayo had probably sent them more information.

Under the moonlight, he scanned the letter - and froze in horrified shock at what he read.

Oh no. This... this was bad.

"Change of plans, Nezuko," he muttered. "We need to get to the Ubuyashiki Estate. Now."

Nezuko tilted her head questioningly.

Tanjirou looked up from the letter, his face pale.

"Tomioka Giyuu is about to be executed by the Demon Slayer Corps. And it's all because of us."

I just watched Mugen Train the other day and... holy hell. I don't have the words to describe it. The movie was just the perfect combination of hype and pure feels.

Just a note: Tanjirou is strong, but he's not that strong yet. Kibutsuji Muzan only fled because of his Yoriichi PTSD/trauma.

Finally, a massive thank you to tuntuntunaa, who was kind enough to help me out with this chapter.

Thank you all for reading, and please review!