Yoriichi Tsugikuni vs Muzan Kibutsuji

Next Battle	Yoriichi Tsugikuni vs Kokushibo
Yoriichi Tsugikuni vs Muzan Kibutsuji
Details
Chapter(s)	187
Place	A bamboo forest
Arc	Sunrise Countdown Arc
Combatants
Demon Slayer Corps Yoriichi Tsugikuni
Demons Muzan Kibutsuji
Powers and Abilities
Yoriichi: Sun Breathing
Muzan: Blood Demon Art
Damage and Casualties
None
1,500 of the 1,800 pieces of Muzan's body is destroyed.

Yoriichi Tsugikuni vs Muzan Kibutsuji is a battle that took place in a bamboo forests nearly 500 years ago during the Sengoku period. It focuses on the battle between the demon progenitor, Muzan Kibutsuji, and the most powerful Demon Slayer in history, Yoriichi Tsugikuni.

Prologue

Yoriichi meets Muzan and Tamayo in the forest

Some time after Muzan finds Michikatsu Tsugikuni, a marked Demon Slayer and a Moon Breathing user, and transformed him into the Upper Rank-level demon Kokushibo, he and Tamayo encounters Michikatsu's younger twin brother, Yoriichi, who was the most powerful Demon Slayer and the creator of the first Breathing Style. Although they have never meet each other, after crossing paths with Muzan, Yoriichi immediately understood that he was born into this world to defeat this man. He senses Muzan's violent intent, comparing it to boiling magma from an erupting volcano, ready to consume everything in its path. Muzan instigates the confrontation by stating that he is no longer interested in a swordsman who utilize Breathing techniques.

Battle

Right after Muzan finished his sentence, he unleashes his arms and outright attempts to kill Yoriichi. Though Yoriichi manages to dodge the attacks, he notices how frighteningly fast Muzan's attacks are and how huge the range is. The bamboo behind Yoriichi are all being cut by the attacks. Yoriichi senses that even a single scratch would kill him, feeling a sense of fear for the first time.

Yoriichi sees Muzan's vital organs.

By seeing into the Transparent World, Yoriichi is able to discern that Muzan has a total of seven hearts and five brains that change position within his body. Seeing his chance, Yoriichi perfected his Sun Breathing technique forms and combines them into a single attack, creating the Thirteenth Form and final form of Sun Breathing. With it, he cuts through all of Muzan's vital organs and overpowers Muzan completely.

Yoriichi asks Muzan a question.

As he tries to regenerate his body, Muzan is stunned to discover he is unable to heal and is forced to hold his severed head in place to keep it from falling off, but it wasn't connecting. Yoriichi realizes that his Bright Red Nichirin Sword would work instantly on the Demon King when he kills him decisively, but before doing so he has a question for him. He asks Muzan, "What is the value of a life to you?", but Muzan remains silent and only stares at him. His face swells dark red, which Yoriichi interprets as anger and believe his words didn't reach him.

Yoriichi's attention is then drawn to Tamayo and notices her eyes staring directly at the dismembered Muzan, not with a look of concern, but with a look of hope and eagerness. Deciding he would deal with her afterwards, Yoriichi approaches Muzan in order to finish him off. However, as he takes a step towards him, he hears the sounds of clenched molars breaking. Suddenly, Muzan's body explodes with great force into tiny fragments. Caught off-guard, Yoriichi immediately cuts 1,500 of the 1,800 total pieces of flesh on spot. The remaining portions are too small. If put together, Yoriichi estimates them to be the size of a human head. They quickly escape to regenerate elsewhere.

Aftermath

Tamayo collapses on the floor and begins to weep while tearing out her hair, angrily cursing that Muzan should have died. She is then surprised that she managed to survive despite saying Muzan's name out loud. Yoriichi approaches her and calms her down before she eagerly informs him about Muzan, how he was the progenitor of all demons and would most likely never appear before Yoriichi again. He asks for her compliance in defeating Muzan, to which she agrees, and allows her to escape.

After Yoriichi return to the Demon Slayer Corps headquarters, he is angrily confronted by the rest of the Demon Slayers for failing to kill Muzan, for letting Tamayo escape, and for Michikatsu's transformation into a demon. As a result, he was banished from the Corps and was demanded to commit seppuku, but the newly assigned Oyakata-sama would not allow it to happen.

Muzan was deeply scarred by this encounter and with Kokushibo's assistance, the two slaughtered anyone who used Sun Breathing, in the hopes of preventing another Demon Slayer that had the power to kill him. They were almost successful and able to nearly exterminate Sun Breathing entirely. Greatly fearful of the man he considered the real demon, Muzan never directly confronted the Demon Slayers again and sent demons to do his bidding for the most part. He remained fearful of Yoriichi even after his death.

Trivia

• This is the first known chronological battle in the series.