Moto Ansatsusha, Tensei Shite Kizoku no Reijou ni Narimashita

The story is about Serena, a former assassin who was reincarnated as a duke's daughter after failing her mission. She initially thought that pretending to be a noble would be easy, but she struggled with the gap in perception between herself and her mother, who had a flighty personality, and her adoptive sister, who deceived those around her in an attempt to push Serena out of the picture.