Romantic isekai

After failing a mission, an assassin is reincarnated into a duke's household. With her memories intact, she continues growing with her cold personality. Her mother adopts a commoner for her bubbly personality, unlike the MC.

This younger sister rlly needs to know her place bro. She keeps using "i was a commoner" as an excuse to avoid her responsibilities and any time MC lectures her about beinging shame to the Violet household

After a car accident with her niece and sister, she isekai's into a fairy tale she read in a book as the abusive sister of the FL, who can cry diamond tears. The book was extremely vague with descriptions, so she doesn't know who the ML of the book is, but she will do anything to get the FL her happy ending.