The author of the novel The Emperor and the Saint faces an unexpected twist: she reincarnates as the mage Fiona Green, the final boss character that she set up to be devastatingly defeated. Seven years before the plot begins, 13-year-old Fiona's cruel family sends her to a near-certain death in the snowy and monster-infested territory of Duke Abel Heylon.

Aware of her unparalleled strength, Fiona aims to serve in the duke's army and eventually lead a normal life. By chance, she encounters the protagonist Siegren, an illegitimate child of the emperor, whose heroic undertakings will soon impact the whole empire. However, reality keeps betraying Fiona's expectations in subtle ways. Her once bitter enemy Abel now dotes on her, and Siegren rises through the ranks solely to remain by her side.

Though unsure what to make of her characters' changed attitudes, Fiona strives for a way to alter her destiny—because despite the story she once wrote, she too deserves a happy ending.