The Shocking Reason Behind Muzan's Obsession with the Blue Spider Lily

The elusive Blue Spider Lily holds the key to Muzan Kibutsuji's cure and has been the center of his desires for centuries. Despite its selective blooming periods, Muzan's relentless pursuit of the flower has yet to yield any results. In the Swordsmith Village Arc, Muzan's fury towards his Upper Moons intensifies as they fail to find the flower as ordered. This leads to an ultimatum for his subordinates to halt the progress made by the Demon Slayer Corps. The Blue Spider Lily's origins can be traced back to the Red Spider Lily of Japanese folklore, which guides souls to their next life. However, the Blue Spider Lily is intended to serve as an instrument of damnation rather than salvation.

The Origins Of Muzan's Ailment

Muzan's life was plagued by poor health and a mysterious terminal illness that threatened to take him before he turned 20. He harbored a deep fear of death and resented the hand he had been dealt. Despite this, a prototype medication developed by a doctor cured him of most of his woes and endowed him with a strong body capable of subjugating those around him with his transformative blood. As the Demon King and progenitor of all demon kind, he drew many to his side to further his ambitions. However, he was unable to go out in the sun without being horribly disfigured and burned, which severely hindered his regeneration. This weakness became his one vulnerability, which he passed on to those under his dominion. Muzan also possessed an intense craving for human flesh, but his lack of empathy allowed him to satiate this need without issue.

Why Is The Blue Spider Lily So Valuable?

Muzan deeply regretted killing the doctor who had cured him so hastily, as he believed that his treatment with the experimental medication was still incomplete at the time. His obsession with the flower's medicinal properties grew, as they were relatively untested and the treatment was nearly impossible to replicate without the only person who knew its composition. The flower was believed to eliminate his weakness to the sun, making him truly immortal and invulnerable to any external attack or element, fulfilling his ambition of living eternally without fear of death. Muzan also sought to create a demon who could withstand the sun's threat and help him overcome his ailment. His murder of the Kamado family was partly motivated by this, as evidenced by how he injected certain members with his blood. Although nearly all of them succumbed to injuries, Nezuko, Tanjiro's younger sister, became a demon herself and was able to overcome the sun's effects, fulfilling Muzan's desire.

How Has Muzan Failed To Attain It?

The Blue Spider Lily proved to be an elusive flower for Muzan to obtain, as it only blossomed during a few instances each year in the daytime. In some regions, it failed to bloom altogether, adding to the difficulty of procuring it. Once the flower bloomed, it would close up and lose its valuable properties, resembling a common weed. Muzan found it challenging to search for the flower himself, so he entrusted his subordinates with the task, despite their vulnerability to the sun. So far, Kie Kamado was the only one known to have knowledge of a spot where Blue Spider Lilies grew, having taken her son there when he was young. As a result, Tanjiro was the only remaining person in the Demon Slayer corps who knew the flower's location, making him an indispensable commodity to Muzan, should he ever try to enlist him.