Yoon Haneul, known for her agreeable nature, wakes up to discover she has transformed into Aila Mertensia, the antagonist from her own novel penned a decade ago. Preferring a leisurely life immersed in books, Haneul's tranquility is shattered as she becomes ensnared in a time loop where each day repeats itself unless she embodies the role of Aila Mertensia. Clueless about portraying a villainess, she receives unexpected aid from the enigmatic warlock Killian, who proposes to guide her in mastering the art of villainy. To break free from the temporal cycle, Haneul must strike a pact with Killian, yet she grapples with doubts about his trustworthiness, pondering if she can truly rely on this charming yet mysterious individual.