In the manga Muzan always demonstrated a deep fear of the Sun Breathing—the first and most powerful Breathing Style. All other techniques, such as Water Breathing, Flame Breathing, and Thunder Breathing, derive from it. Created with the purpose of eliminating demons, this technique stands out for mimicking sunlight, the mortal weakness of these creatures, making it a devastating weapon against them.
The story of the villain Muzan
During the Heian , Muzan was transformed into a demon after a failed experimental treatment for his terminal illness. Realizing he had achieved eternal life, his new goal became securing 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 Sun Breathing technique.
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 brutally underestimated his opponent and was quickly defeated by the Sun Breathing. Before Yoriichi could deliver the final blow, Muzan exploded his own body into a thousand pieces of flesh to escape and regenerate later.
After that desperate escape, Muzan experienced fear for the first time and was tormented 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 on sunlight. Determined to eliminate any threat, Muzan made it his mission to destroy all those capable of using the Sun Breathing technique. After Yoriichi's death, he ensured that no Demon Slayer mastered such a technique, hunting down and killing anyone who showed that potential. Since that traumatic encounter, Muzan never again confronted the Demon Slayers personally—preferring to send his subordinates. This reveals how deeply Yoriichi marked and terrified Muzan's existence.
Muzan and the first encounter with Tanjiro
Tanjiro first encounters Muzan in Asakusa, Tokyo. Recognizing his scent, Tanjiro attempts to confront him, but Muzan disguises himself, transforming a passerby into a demon to create a distraction and fleeing. Terrified, he orders the Lower Moons to eliminate the Demon Slayer with the Hanafuda earrings—the same earrings worn by Yoriichi, the only 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 technique through the Hinokami Kagura dance, and this made Tanjiro a real threat. The technique not only ignores demonic regeneration, but is also the only one capable of fatally wounding Muzan. For this reason, he also ordered the extermination of Tanjiro's family—to erase any trace of connection to Yoriichi and prevent the return of Sun Breathing.
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