Mio Satou is a commoner working odd jobs to pay for her younger sister's treatment for a mysterious terminal illness. After she stops a purse snatcher, she is approached by the purse's owner, Shizuki Sakurazaka, the heiress of the Sakurazaka Group, one of the most powerful conglomerates in modern Japan. Shizuki offers Mio a deal: take her place at an elite academy for three years, and in return, Shizuki will use her family's vast resources to cure Mio's sister.

Mio accepts, but Shizuki then reveals a staggering secret. Their reality is actually based on an otome game from Shizuki's previous life, in which Shizuki herself is the original antagonist—a villainess whose public downfall and ruin are essential to guide the world toward its happy ending. Shizuki has no intention of suffering that fate. Instead, she needs Mio to become her proxy. Mio must assume the identity of the heiress and deliberately act as the villainess, bullying the game's heroine and ensuring the heroine ends up with the correct romantic interest. Mio's mission is to follow the game's plot to her own social destruction, thereby fulfilling the narrative requirements while sparing the real Shizuki. Shizuki cryptically suggests that this charade is necessary for reasons beyond personal survival, hinting that the game's scripted events are tied to the nation's economic stability.

Thrust into the labyrinth of high society, the former commoner Mio must navigate the treacherous three years at the academy while trying to perform the role of a cruel aristocrat. However, she is fundamentally a kind and caring person. Her every attempt to be genuinely malicious backfires, as her inherent goodness leaks through her performance. The other students do not see her as a villain but misinterpret her forced cruelty as the actions of a classic tsundere. This creates a central comedic and dramatic conflict: Mio is trying her hardest to be a terrible person but is constantly undermined by her own conscience, often accidentally helping the heroine instead of hindering her.

The first volume establishes Mio's desperate struggle to force the plot back on its rails. She tries to bully the game's heroine, Nonoka, and alienate the influential male leads, but her actions have unintended, often positive, consequences. A notable early arc involves Mio dealing with two minor bullies who serve as the first obstacles in the game, only to find herself in a position where she must rehabilitate them after her plans go awry. As she stumbles through her role, more perceptive characters begin to suspect there is more to Mio than her villainess facade suggests, while Shizuki lurks in the background, her true motivations and the full scope of her plan remaining a mystery. The first volume covers only the initial months of Mio's three-year ordeal, ending with her beginning to realize that her very presence is altering the game's world in unpredictable ways, and that her path to saving her sister may be far more complicated than simply marching toward her own doom.