Moto Ansatsusha, Tensei shita Kizoku no Reijou ni narimashita.

Serena, a former assassin who dies after failing a mission, is reincarnated as a duke’s daughter in another world. She expects pretending to be a noble to be simple, but finds herself at odds with her flighty mother and her adoptive sister, who deceives others in an effort to drive Serena away. Serena deftly avoids harassment at rivalrous tea parties and navigates a school caught up in love and hatred, yet her cold manner leaves her isolated. When she discovers her adoptive sister is engaged to the second prince, Serena runs away from home. The first prince, Evan, appears before her, beginning a new turn in the life of an assassin who knows little of love.