In the manga Muzan has always demonstrated a deep fear of Sun Breathing—the first and most powerful Breathing Style. All other techniques, such as Water, Flame, and Thunder Breathing, derive from it. Created for the purpose of eliminating demons, this technique stands out for mimicking sunlight, their mortal weakness, making it a devastating weapon against them.
The story of the villain Muzan
During the Heian , Muzan was transformed into a demon after an unsuccessful experimental treatment for his terminal illness. Realizing he had achieved eternal life, his new goal became to secure absolute immortality. However, everything changed when he met Yoriichi Tsugikuni —a legendary Demon Slayer who nearly killed him. From then on, Muzan deeply feared Yoriichi and the dreaded Breath of the Sun.
Despite being incredibly powerful, like all demons, Muzan possessed a fatal weakness: sunlight. When he first encountered Yoriichi—the creator of the first Breathing Technique—Muzan believed he could easily defeat him. However, he grossly underestimated his opponent and was quickly defeated by the Sun Breathing Technique. Before Yoriichi could deliver the final blow, Muzan exploded his own body into a thousand pieces of flesh to escape and regenerate later.
After this desperate escape, Muzan experienced fear for the first time and lived haunted by the memory of that battle. He only returned to direct action when he learned of the existence of Nezuko , a demon capable of walking in the sun. Determined to eliminate any threat, Muzan made it his mission to eliminate all those capable of using Sun Breathing. After Yoriichi's death, he ensured that no Demon Slayer could master this technique, hunting down and killing any who displayed such potential. Since that traumatic encounter, Muzan has never again personally faced the Slayers—preferring to send his subordinates. This reveals how deeply Yoriichi marked and terrorized Muzan's existence.
Muzan and the first meeting with Tanjiro
Tanjiro first encounters Muzan in Asakusa, Tokyo. Recognizing his scent, Tanjiro tries to confront him, but Muzan disguises himself, transforms a passerby into a demon to distract him, and flees. Frightened, he orders the Lower Moons to eliminate the Hunter with Hanafuda earrings—the same ones worn by Yoriichi, the one who nearly killed him. This detail awakens traumatic memories in Muzan and the fear of reliving his worst nightmare.
The Kamado family unknowingly preserved the Sun Breathing through the Hinokami Kagura dance, making Tanjiro a real threat. Not only does the technique bypass demonic regeneration, it's also the only one capable of fatally wounding Muzan. Therefore, he also ordered Tanjiro's family exterminated—to erase any trace of connection to Yoriichi and prevent the Sun Breathing from returning.
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