A plain, unremarkable office worker who spent her middle school years writing a cringey self-insert fantasy novel dies in a sudden accident and wakes up inside that very story. She has reincarnated as Monica, the villainess noblewoman she created. Having written the novel herself, she knows every plot beat in advance. She successfully navigates the standard condemnation event where her fiancé, Prince Fons, publicly breaks their engagement, and she is banished from the kingdom. The story she wrote ends there for Monica, but the reincarnated protagonist carries one regret: she never got to meet her favorite character, Kairi, the edgy dark hero from the enemy kingdom whom she filled with every melodramatic, chuunibyou trait she could dream up.

While traveling to a neighboring country to find work and a new life after her exile, Monica is attacked by bandits on the road. At the last moment, a man appears and rescues her. He is Kairi, the very character she most adored and never expected to see. Instead of a simple rescue, Kairi makes her an unexpected proposition: a fake marriage. He needs a bride to maintain appearances within his own complicated court, and Monica, who knows his entire backstory because she wrote it, seems like the perfect candidate. She accepts, and what was supposed to be a closed chapter becomes the start of a new one inside the world of her own black history.

The story unfolds in a fantasy kingdom with magic, imperial courts, and political intrigue, all built from the narrator's teenage imagination. Monica finds herself living in Kairi's castle, and her foremost goal shifts from mere survival to rewriting his fate. She knows from her own writing that Kairi is destined to die. Determined to save him and give him a happy ending, she uses her knowledge of the original plot to navigate dangers, avoid flags that lead to tragedy, and strengthen her bond with him. Their initial cold contract relationship gradually warms as Kairi, who was written as a lonely and misunderstood figure, responds to her genuine care. Monica also confronts the complications of being the creator inside her own creation, meeting her original heroine and former fiancé again and deciding how much of the original story she is willing to let play out. The narrative balances her mission to save Kairi with the romantic and physical development of their relationship, all framed by the comedic embarrassment of having to live inside the overwrought fantasy she wrote as a teenager.