Muzan was drugged by the demon doctor Tamayo, with crucial help from Shinobu Kocho and Yushiro, using a powerful, multi-stage "Anti-Kibutsuji Drug" designed to weaken him for the final battle, eventually turning him human and destroying his cells, as explained in the Demon Slayer Wiki.
Before Kagaya Ubuyashiki and his family sacrificed themselves in a suicide attack to stun Muzan, Tamayo assimilated some of the drug herself, so that if the likely possibility that Muzan would absorb and assimilate her body occured, the Demon King would also take in the drug on accident.
Despite becoming blind in both eyes due to the progression of his illness, Kagaya immediately sensed the presence of the number of individuals with Hashira-level power upon arrival and expressed his satisfaction that they all made it to the meeting without personnel changes.
Demon Slayer enthusiasts are buzzing about the connection between Tanjiro Kamado and the formidable Upper Moon One, Kokushibo. While not directly related, Tanjiro is seen as the spiritual successor to Yoriichi Tsugikuni, Kokushibo's twin.
After the realization of what she had done to her family sunk in, she fell into a void of despair. It is hinted that at some point in her new life, Tamayo had attempted to kill Muzan to avenge her family and as revenge on him for turning her into a demon, a battle she lost.
The only canonically LGBTQ+ character in Demon Slayer is Suma, one of Tengen Uzui's wives, who is confirmed to be bisexual and polyamorous in the series' databooks, showing affection for both men and women, including Tengen and her fellow wives, Makio and Hinatsuru. While other characters like Mitsuri are speculated to be queer, Suma is the sole officially confirmed character, with her relationship dynamic highlighting both bisexuality and polyamory within the Demon Slayer Corps.
Shiko Kibutsuji (鬼舞辻 死子, Kibutsuji Shiko?) is Muzan Kibutsuji and Enmu Kibutsuji's eldest daughter and the youngest of their two children. She is currently their only biological child.
Muzan Kibutsuji's motivation to kill Tanjiro's family was to create a demon immune to sunlight, fulfilling his desire to be unstoppable. Nezuko's transformation into a demon immune to sunlight ultimately backfired on Muzan, leading to his ultimate downfall in Demon Slayer.
Swordsmith Village Arc
After falling into a coma in the aftermath of his battle against Upper Rank Six, Tanjiro Kamado dreams of memories belonging to his ancestor Sumiyoshi. Within them, Yoriichi is seen holding a newborn Sumire as her mother sleeps.
Kaigaku and Zenitsu are not blood relatives but were disciples under the same mentor, Jigoro Kuwajima.
While many Hashira died in the fight, some survived: Giyu Tomioka, the Water Hashira, and Sanemi Shinazugawa, the Wind Hashira, both survive the final fight, carrying on the memory of their fallen comrades. Tanjiro also survives, and after the war, the Demon Slayer Corps disbands because demons are gone for good.
There's no single "worst" character, as it's subjective, but top contenders for hated or disliked characters often include the sadistic demon Doma (Upper Rank Two) for his cruelty and killing of Shinobu's sister, Muzan Kibutsuji for being the source of all evil, and sometimes Kaigaku, a traitorous Demon Slayer, with some viewers finding Zenitsu annoying due to his constant screaming, though many defend him.
Nezuko's immunity to sunlight in Demon Slayer may come from eating the Blue Spider Lily, as shown in the anime's finale. The Blue Spider Lily's significance adds depth to Muzan's failure, highlighting his contempt for humanity in the series.
Muzan rationalizing his crimes to Tanjiro and Giyu in his most infamous speech. Muzan Kibutsuji (鬼舞辻無慘, Kibutsuji Muzan), also known as the Demon King, is the main antagonist of the Demon Slayer: Kimetsu no Yaiba franchise.
The only canonically LGBTQ+ character in Demon Slayer is Suma, one of Tengen Uzui's wives, who is confirmed to be bisexual and polyamorous in the series' databooks, showing affection for both men and women, including Tengen and her fellow wives, Makio and Hinatsuru. While other characters like Mitsuri are speculated to be queer, Suma is the sole officially confirmed character, with her relationship dynamic highlighting both bisexuality and polyamory within the Demon Slayer Corps.
Swordsmith Village Arc
As he sleeps, recovering from the injuries he acquired during his fight with Gyutaro and Daki, Tanjiro sees a fragment of a memory inherited from Sumiyoshi. In it, Sumiyoshi was shown interacting with Yoriichi, who had visited his house during his second child's birth.
Kanae Kocho, Kyojuro Rengoku, Tengen Uzui, and Shinobu Kocho were the only Hashira of the Taisho Era to never awaken the Demon Slayer Mark. In Tengen's case, it was because Tanjiro had not yet awakened his Demon Slayer Mark, and as such there was no precursor he could come into contact with to help activate it.
Muzan has always been a rational character, but fans believe killing his doctor is the only time he regretted taking a life.
Hinokami Kagura (ヒノカミ 神楽 かぐら , Hinokami Kagura?): Tanjuro was capable of using the Sun Breathing as the Hinokami Kagura taught from his own father, passing down the dance and Yoriichi's earrings to his son.
Though Tanjiro can be annoyed by Zenitsu's tantrums and womanizing behavior, he cares for Zenitsu as a close friend and is very patient with him. Zenitsu tends to be the one to inform Tanjiro of the city life and occasionally explain things due to Tanjiro's naivety.
Nakime, Daki, Mukago, and Ubume are the only known members of the Twelve Kizuki who are female. Gyutaro and Daki are the only members who are biologically related to each other, as they are brother and sister. Kokushibo and Kaigaku are the only members who were formerly Demon Slayers.
Also the reason why Nezuko was already so powerful is because Muzan injected tons of blood in her body and the others in hopes of creating a demon that could conquer the sun.