My Daughter Has Become A Fool

Reincarnated as 'Extra 1' in a romance-fantasy novel, the protagonist finds herself as the adopted daughter of the main villain. This villain, years later, is destined to sacrifice his daughter, a fate the protagonist aims to avert. To become indispensable, she proposes a radical image makeover for the Duke of Schlager family, suggesting they adopt a "daughter's fool" concept. This strategy transforms the Duke and his two older sons, who embrace the "younger sister's fool" persona. Gradually, the villainous family's reputation shifts, with rumors spreading about the Duke's kindness to his adopted daughter and surprise at his benevolent adoption of an orphan. This positive change surprisingly aids the Duke's business endeavors. However, the implemented personas extend beyond public appearances. The Duke insists on reading fairytales to his daughter to boast about it later, and the older brother, tasked with the "sister's fool" role, offers calculated protection at home. Even the youngest brother, meant to embody a tsundere concept, struggles, finding his adopted sister unexpectedly endearing. The protagonist questions why this villainous family operates so unusually.