Demon Slayer: Kimetsu no Yaiba season 3 revealed that Nezuko is immune to sunlight, an ability unique to her. While the manga never explained this, the anime hinted that her immunity may come from eating the Blue Spider Lily. This theory is supported by the second databook, which mentions the flower near Nezuko's home. This revelation also sheds light on Tanjiro's similar immunity, tying up loose ends in the story. As Muzan learns of Nezuko's immunity, the focus shifts to protecting her from his grasp. The final battle between demons and Slayers looms, with Nezuko's importance increasing.

Other mysteries the anime could explore include the origin of the Demon Slayer Marks and Genya Shinazugawa's powers. The Blue Spider Lily's significance adds depth to Muzan's failures, showcasing his disdain for humanity. The anime's potential to address these mysteries further enhances the world of Demon Slayer: Kimetsu no Yaiba.