Demons overrun the world as new generations of heroes must establish their own legend. You're not the destined heroine or even her elegant rival—you're simply the contemptible third female lead, condemned to fade into obscurity. Upon transmigration into this dangerous realm, a system binds itself to you with a singular objective: seduce the male lead. Yet your actual target proves far more sinister: the female lead's beloved younger brother. This man—a yandere consumed by obsessive devotion to his own sister—conceals a twisted psyche and ruthless brutality beneath his composed exterior. With the heroine, hero, and this possessive brother all serving as demon slayers, you find yourself ensnared in a web of forbidden desire and hidden malevolence. To survive this treacherous game of manipulation and obsession, you must transcend your role as expendable cannon fodder and become something far more dangerous, forcing your way into a destiny that was never meant to be yours.