One of the biggest unresolved mysteries in Demon Slayer: Kimetsu no Yaiba was why Nezuko was uniquely immune to sunlight, unlike other demons. This was never explained in the manga or even in supplementary databooks.
However, the anime’s recent season 3 finale may have finally provided an answer through Tamayo’s blood analysis revealing Nezuko has traces of the mystical Blue Spider Lily in her veins.
The Blue Spider Lily is known to have special properties that could potentially cure Muzan of his weakness to sunlight. So the anime could be hinting that Nezuko inherited an immunity through exposure to the Blue Spider Lily’s powers early on.
Interestingly, one of the Demon Slayer guidebooks indicates Muzan had sought the Blue Spider Lily to overcome the limitations of demon physiology.
So Nezuko gaining sunlight resistance from the flower would be a poetic irony, as well as a sensible explanation for her unique biology that eluded fans for so long.
The season 3 climax provides a plausible contributory factor from existing lore to illuminate why Nezuko transcends typical demon weaknesses in sunlight.
If this fan theory is true, it would resolve one of the manga’s hanging plot threads at last through the clever use of established story elements.
Nezuko’s Sunlight Immunity
The theory that Nezuko gained sunlight immunity by ingesting the rare Blue Spider Lily seems increasingly credible given additional lore from Demon Slayer supplementary materials.
The second official databook reveals that Tanjiro’s mother showed him a secret place near their home where the mystical flowers bloomed. Intriguingly, the same book states Tanjiro was the only Kamado child who witnessed them in bloom.
However, that does not preclude his siblings like Nezuko from seeing the dormant Blue Spider Lilies at other times.
It is quite plausible that Nezuko could have encountered and eaten one of these unique flowers known to have demon-enhancing properties. This would later manifest as sunlight resistance after her transformation.
The databook even establishes the Blue Spider Lily as geographically accessible to the Kamado siblings. So Nezuko opportunistically consuming one, perhaps curious over her brother’s sighting, neatly explains her special physiology without contradicting the existing backstory. It adds deeper resonance to Tanjiro’s personal connection to the flower’s lore as well.
Tanjiro’s Sunlight Immunity and Muzan’s Cunning Scheme
The Blue Spider Lily consumption theory also clarifies another late-stage twist in Demon Slayer’s climax.
As Muzan nears death, he spitefully turns Tanjiro into a demon to carry on his legacy, remarkably with full sunlight resistance just like Nezuko. This shocking development originally had little justification beyond Tanjiro’s sibling connection to Nezuko.
However, if her immunity indeed stemmed from ingesting the Blue Spider Lily, it logically follows that Tanjiro would have resistance as well through the flower’s enduring effects.
Given the databook’s statements about the Kamado family’s closeness to the Lilies, Tanjiro likely visited the blooms with his mother too. He could have easily sampled one out of childish curiosity.
This would imbue Tanjiro with the same protective properties that later translate into sunlight immunity as a demon. It makes far more narrative sense than both Kamado siblings randomly manifesting the same ultra-rare condition independently.
In essence, the Blue Spider Lily presents a reasonable unifying explanation for both Tanjiro and Nezuko’s anomalous abilities to exceed standard demon weaknesses.
This clarifies Muzan’s endgame scheme as specifically targeting the Kamados for their existing affinity with the Lily instead of an unforeseen coincidence. It transforms an abrupt, rushed plot twist into a clever full-circle callback to Demon Slayer’s established magic system.
Muzan’s Downfall and the Unseen Legacy of the Blue Spider Lily
The Blue Spider Lily theory lends even more profound irony to Muzan’s ultimate downfall. As the final Demon Slayer chapter reveals, the coveted flowers Muzan sought for centuries only bloom during daytime – something impossible for him to ever witness personally.
Yet the Kamado siblings he turned into demons gained that coveted resistance seemingly by virtue of their family’s generational ties to the Lilies.
If Nezuko and then Tanjiro inherited sunlight immunity from human contact with the flowers, it underscores how Muzan was thwarted by the very humanity he so despised.
Despite all his power, he never grasped how human traits like love and memory allowed the Blue Spider Lily’s secrets to be quietly passed down within the Kamado lineage. So, in the end, his contempt for humanity bred the ignorance that doomed his quest for perfection.
Muzan’s incapability to appreciate humanity even prevented him from fully understanding himself, as tracing his origin reveals.
Muzan became a demon through experimenting with an elixir mixing Blue Spider Lily components – the natural culmination of very human pursuits like scientific curiosity and the desire to heal illness.
Ironically, embracing his remnants of humanity rather than erasing them might have granted him the perspective to achieve his immortal aims.
