A Japanese otaku and hikikomori dies protecting a child from a car accident and reincarnates in a fantasy world as Yumie Granbell, the extraordinarily beautiful young daughter of a count. Looking into a mirror, the protagonist sees a girl who resembles an angel and will surely grow into a stunning woman. The Granbell family is a prestigious and influential magical house with considerable wealth and a powerful private army, leading the protagonist to believe they have hit the jackpot.

However, this dreamlike situation quickly shatters. Yumie is an illegitimate child and is severely mistreated within the household. Upon cheerfully greeting her mother, she receives a painful slap and is yelled at for being noisy. The protagonist soon realizes that their own existence is the cause of the family's decline. The strained relationship between Yumie's parents has deteriorated to the point of daily arguments, pushing the entire Granbell family to the verge of collapse.

Determined to save her new family, the protagonist decides to use Yumies peerless cuteness as a weapon. The goal is to bring smiles back to the family, resolve the conflicts, and restore the Granbell name to its former glory. The story follows Yumie's efforts to navigate noble society and family politics, aiming to become a beloved character and fix the problems her very existence inadvertently created.