In an era where the demon king Tantai Jin rules and inflicts misery upon humanity, the immortal elders decide to send someone back in time 500 years to prevent his awakening by destroying his demonic bone. Li Susu, the daughter of the Hengyang Sect leader, accepts this perilous mission, transforming into Ye Xiwu, the mortal wife of Tantai Jin before he becomes fully corrupted. Bound by mortal identities, Susu struggles to balance her divine mission with unexpected empathy for the bullied, unawakened Tantai Jin. As their fates intertwine across multiple realms—including mortal, immortal, and dream realms—both characters must confront profound betrayal, sacrifice, and deep-seated trauma. The central conflict forces Susu to choose between completing her duty to eliminate the world's greatest threat and saving the man she has slowly grown to love.