Moto Ansatsusha, Tensei Shite Kizoku no Reijou ni Narimashita

The story follows Serena, a former assassin who gets reincarnated as a duke’s daughter after failing a mission. At first, she assumes playing the part of a noblewoman would be simple, but she quickly realizes how different she is from her carefree mother and her scheming stepsister, who tries to manipulate others to push Serena aside. Though she skillfully avoids the petty rivalries at tea parties and navigates the complicated social dynamics of her school, her aloof personality leaves her isolated and shunned. When she learns her stepsister is engaged to the second prince, Serena decides to flee—only to cross paths with the first prince, Evan.