The breadth and antiquity of Iranian mythological traditions have made it difficult to uncover their underlying mythic structures, causing some interpretations to remain confined to the narrative surface or to moral evaluations. Consequently, understanding the logic governing the actions of mythic characters requires a mythological and structuralist analysis. Adopting a comparative approach, this study examines the figures of Jehikā in the Bundahišn and Arnavāz in the Shāhnāmeh—two characters who, at first glance, appear fundamentally different, one embodying a demonic nature and the other an Ahuric one. The findings demonstrate that, despite this apparent contrast, Jehikā and Arnavāz represent manifestations of a shared and ancient mythological pattern. Within this pattern, the dark-natured woman (peri) awakens a dormant demonic force, thereby precipitating an assault upon the Ahuric world and the death of the primordial beings. Subsequently, however, through her love for a luminous male figure, she severs her ties with the forces of darkness and aligns herself with the powers of light, thus contributing to the eventual defeat of evil. This union not only facilitates the transfer of political authority but also releases fertility and prosperity into the world, although it ultimately culminates in a tragic fate for either the male protagonist or the offspring born from the union. By elucidating the common deep structure underlying these two narratives, this study highlights the active and decisive role of the dark-natured woman in the dynamics of darkness and light, the transmission of power, and the continuation of creation within the Iranian worldview.