The blue spider lily is an essential ingredient in the medicine that turned Muzan into a demon. The flower only blooms during the day for two to three days per year.
Muzan's ultimate goal is to attain an immortal body. He wanted to be able to walk in the sunlight and live forever. In order to gain this, he needed two things: the Blue Spider Lily and the body of a demon who could withstand the sun.
It was then that Muzan realized the medicine actually had effect: he obtained a strong body, but due to the medicine being a prototype, he consequently could not walk into the sunlight and crave human flesh, turning him into a Demon.
This makes Muzan make Nezuko his primary target, as he needed a demon who could withstand the Sun. Ultimately, Muzan was never able to find the Blue Spider Lily before his death at the hand of the demon slayers.
It is also implied that the Blue Spider Lily can nullify a demon's weakness to the sun if it's consumed, which is the reason Muzan was spending centuries searching for the flower.
Nezuko's Sunlight Immunity in Demon Slayer is Tied to the Blue Spider Lily. Nezuko having eaten the Blue Spider Lily at some point could explain her immunity to sunlight, and Demon Slayer: Kimetsu no Yaiba has already worked to justify that.
The two known demons who broke free of Muzan's curse are Tamayo and Nezuko. Tamayo was able to break free of the condemnation when Yoriichi fought Muzan, nearly killing him in the process.
Since Nezuko is from a Sun Breathing lineage, she can survive in daylight. After the final battle against Hantengu concludes, she can step into daylight, and many theories are available about the phenomenon. One of the theories is that her abstinence from consuming human blood is what saved her.
The blue spider lily is an essential ingredient in the medicine that turned Muzan into a demon. The flower only blooms during the day for two to three days per year. After that, it closes up and looks like a huge horsetail weed. The Blue Spider Lily doesn't bloom at all, depending on the climate.
Both are blood-red in color and grow in clusters. A Red Spider Lily's bulb is poisonous and commonly associated with death in Japanese legends. It is shown that Kie Kamado, Tanjiro's Mom, knew when the blue spider lily bloomed, and she even showed Tanjiro when he was younger.
In a nutshell, Muzan, being the progenitor of demons, is not scared of Doma. However, he is irritated by his inability to decipher Doma's thoughts and feelings, which is the ultimate control he has over all of his creations. Upper-Rank Two: Doma is a nihilistic maniac and a misanthropic cold-blooded demon.
This is shown in one of the last chapters of the manga when Muzan is dying. He shows his most human side to fans, wherein he admits to regretting murdering his doctor. He comments that had he been patient, the doctor would have cured him, and he would never have turned into a demon.
Thus, Muzan created demons for hundreds of years even when he didn't want to turn someone. Since he didn't know anything about the Blue Spider Lily medicine, he needed others to find the plant for him by happenstance. This is the general reason why Muzan turned Nezuko into a demon.
Therefore it is quite evident that Muzan doesn't love his family. They are merely tools to achieve his goal of true immortality and wreak havoc in the years to come.
Muzan's backstory summarized
Ever since he was a baby in the Heian Era, Muzan Kibutsuji was always stricken with illness and thanatophobia, or fear of death. According to the Demon Slayer manga, his heart stopped multiple times in the womb, but he only escaped cremation by crying.
Ultimately, Yoriichi is the only being Muzan ever feared as he personally saw him as the true "monster" between the two of them and to the very end he remained baffled as to how a being like Yoriichi came to exist.
His main outfit in this disguise is a plain white button-up shirt and black cargo shorts with long tube socks and loafers. After he neutralizes Tamayo's poison and emerges from his flesh cocoon, Muzan's hair grows in length and turns white due to Shinobu's poison accelerating his age.
For those who have watched only the first season of the anime, they will be surprised to know that Muzan turns into a woman in the second season. He keeps transforming in order to hide his true identity, and he's even known to change into an 11-year-old child to hide from Demon slayers.
A generous doctor from the Heian Period cursed him with demonic powers, transforming him into a devil. Muzan then injected Tanjiro with his blood, turning him into a demon as well. Muzan's power is so great that those who have been injected by him become his slaves, and he is able to pass on his dream to Tanjiro.
Secondly, Muzan would probably… eat Nezuko and Tanjiro in the hopes of obtaining their sun-resistance abilities, and also since he wouldn't be able to convince them to become demons to work under him. This would allow him to become the ultimate demon.
Tanjiro used Thunder Breathing during their battle with the fourth Upper Moon, Hantengu, to cut some distance between him and the latter. This moment came out of nowhere and caused a lot of hype online.
At the end of the Swordsmith Village Arc, Nezuko's evolution completes, and she becomes the only demon that can survive in sunlight. At that point, she regains the ability to speak.
Muzan Kibutsuji (鬼舞辻無慘, Kibutsuji Muzan) is the main antagonist of the Demon Slayer: Kimetsu no Yaiba fantasy action manga and anime series. Muzan is the powerful Demon King, who has the ability to inject his victims with blood that allows him to convert them into more demons.
Does Muzan have a favorite demon? Despite the fact that Muzan. is always shown to have disdain for his creations, Muzan does in fact have a favorite. On that list is Naki, made due to a convenient blood demon.
Why did Muzan cry at the end? The manga explains that Muzan found Tamayo four centuries ago when she was begging him to cure her of her illness. He turned her into a demon without telling her, and she went crazy. She mercilessly massacred her own family and after she was done, she cried for her loss.