An orphaned thief named Rosalia lives a desperate existence, surviving by picking pockets until she is finally captured and thrown into a prison cell. Cursing her miserable fate, she is visited by a mysterious girl who calls herself a witch, Meldy. Meldy possesses a singular and terrifying magical ability: the power to rewind time. Rosalia seizes this opportunity without hesitation, using Meldy's power to escape her life of squalor by manipulating the past. She orchestrates her own adoption into a noble family, setting her sights on the ultimate prize, the queen's throne.

The story follows Rosalia as she transforms from a starving street rat into a ruthless and ambitious noble. Driven by a pathological desire for glory, known as megalomania, she is the true villain of the narrative, described as strong, cruel, and relentless. To secure her position and become the prince's bride, she must eliminate all rival noble daughters. Using Meldy's time travel magic, she repeatedly rewinds events to deceive, manipulate, and murder anyone who stands in her path. Her traumatic first life and the experiences of her do-overs gradually twist her into a person who places her own happiness above the lives of others, even as she loses touch with what true happiness really means.

The narrative takes place in a dark fantasy setting defined by courtly intrigue and social climbing. As Rosalia rises through the ranks, she enters a convent for bride training to become queen. Here, she faces new obstacles including a superhumanly strong female swordsman named Katia. Her true nemesis arrives in the form of Pamela, a detective from the Koumakai, an organization dedicated to logic or the arcane. As Pamela investigates, her schemes intersect with those of a boy named Simon, who has infiltrated the convent. The plot deepens further with the emergence of the Thorn Sister, a murderous figure revealed to be connected to a character named Kanna, whose hidden past and obsessive love spiral into a new tragedy.