Till Daybreak

As Hiroto and Tanjiro kept fighting Muzan with everything on the line, trying to keep him from running away until dawn arrived, Rengoku was in an alleyway with Zenitsu, Kanao, and Inosuke, tending to their wounds with other Demon Slayers.

"Those two are amazing. They're able to pressure Muzan, giving their all to this fight." A Kakushi tending to Zenitsu commented, barely able to see the movements from Hiroto and Tanjiro.

Rengoku smiled and said, "They might just be the best Demon Slayers we have ever seen. Not just in power, but the sheer willpower they've displayed."

"Just what kind of breath are they using? I've never heard or seen the breathing techniques and forms they are using." Murata said.

"Hm, Hiroto and Tanjiro call it the Dance of the Fire God, although officially it's called the Breath of the Sun. They said that it was passed down to them." Rengoku answered.

"Passed down? Wait, I remember Tanjiro telling me that he came from a family of charcoal burners." Murata said with a confused expression.

"Haha, I had the same reaction as you. They must have been the most fearsome family of charcoal burner to ever exist." Rengoku joked.

Murata leaned out of the alley and saw Tanjiro and Hiroto get slashed across their body from another of Muzan's attack, ignoring the pain and just kept pushing on.

"They're incredible. Maybe that's what separates us from Hashira's. Tanjiro is Hiroto's little brother, so it makes sense for him to be this strong as well." Murata mumbled.

Rengoku had a proud expression, saying, "Those two are really incredible. They've been fighting for the sake of their sister and each other since the beginning. Haha, I remember the first time I saw them at the Hashira meeting. Shinazugawa did something that caused Hiroto to blow a fuze, attacking him."

Murata paled at Rengoku's words and asked, "Are you kidding? He attacked the Wind Hashira in front of all the other Hashira's?"

Rengoku laughed, "Haha, that's right. The more amusing thought is that Hiroto managed to actually beat Shinazugawa, hahaha."

Murata didn't dare comment, not wanting to risk Sanemi overhearing them.

*BOOM*

A loud crash nearby took everybody's attention, as they saw Tanjiro crash into a wall, ignoring the pain, and rushed forward to assist his brother.

'They're trying to accomplish the 13th form.' Rengoku thought to himself, remembering back to the day they discussed about the Breath of the Sun having 13 forms.

-----

In the Butterfly Estate, Hiroto, Tanjiro, and Rengoku were seated together. Hiroto was braiding Nezuko's hair when Rengoku said something that caught his attention.

"Huh? 13 forms?" Hiroto asked with a confused expression. "We don't know anything about 13 forms. We only know 12 official forms for our Dance."

Rengoku turned to Tanjiro, who also had the same confused looking face.

"From what my father had told me, the Breath of the Sun, or as you like to call it, Dance of the Fire God, has 13 forms. Father told me that in the records, it doesn't specifically say what the 13th form was, just that it exists and is very powerful." Rengoku explained.

"Hmm, 13 forms…" Hiroto mumbled, with Nezuko playing with a glass case filled with goldfish she took from Shinobu. "I'm not sure what this 13th form is."

"Ah, hold on a second, brother." Tanjiro suddenly spoke up. "Do you remember how father was able to keep dancing the whole night in the freezing cold, without stopping once?"

"Yes?" Hiroto answered.

Tanjiro continued. "Since he never stopped, doesn't that mean that he kept performing all of the forms in sequence?"

Hiroto's eyes widened as he said, "You're right. Maybe this 13th form is just all the forms performed in one single sequence."

Tanjiro then said, "It could be, but that sounds insanely difficult. It's already hard enough to do our Dance, let alone do them all one after another."

Hiroto agreed, saying, "Yeah, but who knows. There might come a day when it would be needed."

-----

Back to the fight, Hiroto and Tanjiro pressed on, pushing Muzan back with everything they've got.

'What's happening to me? Why am I getting slower?' Muzan thought, sending his consciousness inside of himself and searching through Tamayo's memories.

What he saw through her eyes were Yuchiro and Shinobu inside of a room fitted with different kinds of medical and research equipment.

"Let's try creating a hybrid drug, in case the original drug itself will decompose," Shinobu said towards Tamayo. "The first effect should turn him back into a human, and if that doesn't work, we should create something with the remaining drug that will have a stronger effect."

"An aging drug is ideal for the second effect. If we use what you created, Tamayo, then we can age Muzan by fifty years per minute."

Muzan's consciousness went back to his body, as Hiroto and Tanjiro charged forwards, cutting off his spikes/

'I've been continuously aging. My power was being chipped away to stave off the aging progression. That's why I was having trouble with those Demon Slayers earlier, including the Hashira's.' Muzan thought, realizing that Hiroto and Tanjiro have been avoiding more and more of his attacks.

'The drug was likely working for over three hours, which means that I have aged by nine thousand years!!' Muzan came to a realization, realizing that his hair was white the entire time.

"Cawww!! Fifty-nine minutes until dawn!!" A crow shouted as Muzan killed it.

'Dance of the Fire God, Flame Dance'

Hiroto performed the last move of the sequence, performing a two-combo strike, starting with a vertical slash then followed by a horizontal, arriving in front of Muzan.

"Stop moving around!!" Muzan yelled out, whipping his spikes towards Hiroto's back.

Tanjiro rushed forward and cut off the spikes before they reached Hiroto with his last sequence as well, allowing the two to fully perform the 12 moves in conjunction.

"Brother, I can't fully grasp it all yet. I think we need to aim for his hearts and brains." Tanjiro said.

"I see," Hiroto muttered as he used the see-through world, allowing himself to see through Muzan's body and locate his hearts and brains.

Tanjiro tried the same method but realized his vision was turning darker. 'I can't see!! I'm lacking oxygen!! Calm down!! Sniff him out. You'll be fine. You can do this for sure!! Just support brother, until dawn…'

As Tanjiro ran forward, Hiroto noticed something wrong with him as Tanjiro's movements seemed off. Then, as Tanjiro was about to perform his next move, his footing slipped.

Taking this chance, Muzan launched his attack while Tanjiro was off balance.

*swish*

*BOOM BOOM BOOM*

A snake-like figure charged forward, grabbing Tanjiro and dragging him away as the surrounding buildings got crushed by Muzan's attacks.

"Iguro!" Hiroto shouted as he saw Obanai with his eyes clawed out and holding Tanjiro.

"Iguro, your eyes! All because you protected me!" Tanjiro said anxiously.

"Wrong! They got injured a while ago. You never shut up about other people. Hiroto! Don't let up, keep attacking!" Obanai shouted towards Hiroto.

Seeing Tanjiro safe, Hiroto charged towards Muzan as he was still trying to kill Tanjiro. Being able to see his hearts and brains, Hiroto directed his next attacks towards them.

'Dance of the Fire God, Thirteenth Form.'

Hiroto continuously performed all twelve styles in succession, dodging and slicing his way towards Muzan. Hiroto jumped past a series of attacks, leaving the ground with deep impressions all around him from Muzan's strikes.

From above, Obanai jumped down towards Muzan and aimed his attack towards his neck. Muzan quickly reacted and swatted his hands towards him.

Obanai, being blinded, was still able to predict the path of the attacks as he dodged out of the way with the help of his snake around his neck, telling him where the attacks were coming from.

As Hiroto got closer, Muzan's body underwent a change. Scars started to appear all over his body, leftover from his battle against Yoriichi.

'Those are the wounds left behind if we follow those we'll have an easier time landing our attacks.' Hiroto shared the same thought as the rest.

"Forty minutes until dawn!!" Another crow came and screamed out.

As Tanjiro was about to land a hit on Muzan, Muzan disappeared from his position, kicking up the dirt as he ran away.

"Stop him! He's running away!" Hiroto shouted towards Tanjiro and Obanai, seeing Muzan trying to run away in the distance.

As Muzan ran forward, he trampled upon the dead bodies of the Demon Slayers, crushing and slicing them apart along the way. Seeing this, Tanjiro seethed with rage, grabbing a handful of Nichirin swords and throwing them towards Muzan.

Just barely having enough time to react, destroyed the swords, causing him to stop his run.

'These persistent pests!' Muzan shouted inwardly.

'Dance of the Fire God, Flash Dance'

Hiroto surged forward, destroying the ground beneath him as he approached Muzan almost instantly and swinging his sword downwards. Muzan raised his arm to defend against the strike, but the sword sunk into its flesh, instead of passing through it.

"Grahhh!!" Muzan cried out, as the searing hot pain from Hiroto's sword burned through his arm. Hiroto gave a sly smile as Obanai dropped from above, stabbing his sword through Muzan's neck.

Using this chance, Hiroto punched his left hand forward towards Muzan's body.

*THUD*

The force behind it was overwhelming, almost causing Muzan to double over as he used the spikes on his legs to stab towards Hiroto's head. Seeing the spikes coming, Hiroto dodged out of the way, pulling his sword out as Tanjiro came forward and swung his sword in a circular arc.

Muzan gritted his teeth and knocked Obanai off his back and dodged Tanjiro's strike.

"Iguro, please! Take this!" Tanjiro shouted, throwing a handful of Yuchiro's talismans towards him, "Use your vision in tandem with Kaburamaru and-"

*WHOOSH*

In anger, Muzan swung both of his arms downwards, crushing the space between Tanjiro and Obanai, cutting them in the process.

"Gagh!/Gh…" Tanjiro and Obanai coughed out, blood spurting from their bodies.

Hiroto jumped forward and grabbed the paper in the air and stuck it onto Obanai's forehead.

"Use these!" Hiroto shouted, turning to deflect a sneak attack from Muzan.

Being able to see better, Obanai weaved forward like a snake, dodging Muzan's attacks as Tanjiro and Hiroto surrounded him.

"Corner him!! Attack him from three sides!" Hiroto shouted, with Tanjiro and Obanai attacking from Muza's side and back.

"Haah. Hah. Haah." Muzan breathed for air, as he started to feel his stamina nearing its limits, with the flesh of his body starting to rot.

As the sounds of battle reverberated through the city, outside of the city, a young girl was running forward, clutching her right eye.

*huff huff* From the outskirts, the familiar figure of Nezuko approached the city, her right eye turning back to a human's, while her left was still that of a Demon. Tears fell from her right eye as she looked towards the chaos in the city.

Nezuko muttered to herself. "Tanjiro… Big brother…"