Muzan Kibutsuji



 Muzan Kibutsuji (鬼舞辻 無惨, Kibutsuji Muzan) is the series' main antagonist who used his blood to sire the other demons, able to manipulate his cellular structure from manipulating his physical form like frequently disguising himself as different humans of various ages and genders to programming transplanted cells within demons he directly sired to destroy a host body if they mention him by name. He also can devour the cells of others to assimilate their abilities and memories. Muzan was originally a sickly young man from the Heian period whose transition into a demon was the result of an experimental treatment to prolong his life, killing his doctor before realizing it worked. He since dedicated himself to "complete his treatment" and become perfect by siring demons that would help him achieve his goal. He also expressed a justified concern towards those who utilize the Breath of the Sun technique since his near death experience from fighting Yoriichi Tsugikuni, which motivated him to slaughter Tanjiro's family as part of an attempt of turning them into demons that are naturally immune to sunlight. Nezuko, the only survivor of the incident, eventually manifests that ability with Muzan focusing his efforts to capture and devour her to remove his only weakness. But the Demon Slayer Corps exploit Muzan's obsession to lay a trap for him which kills his remaining followers, Muzan killing Tamayo and many Demon Slayers before eventually learning that he was infected with a variation of the humanity-restoring serum that Tamayo and Shinobu developed with added poisons that remove most of his abilities and weaken him to be easily killed. This results with his body being destroyed by the sunlight when he is held back by the Demon Slayers to prevent him from escape. Muzan's final act of revenge is to turn Tanjiro into a new demon so he would kill the Demon Slayers, which is thwarted when the boy turns back to human with his friends' help.