Cassmire: The Loyal Sword

During her youth, Kashumir worked as a mercenary to procure medicine for her half-sister Aria. After completing a mission and returning home, she falls and hits her head, which triggers a recollection of a past life where she was reincarnated into the story "The Night of the Fairy." In this reverse-harem novel, Aria was the protagonist, and Kashumir played a villainous role responsible for her suffering. However, Kashumir can't bear to see her sister in agony and vows to protect her until she is adopted by the noble family mentioned in the book. As the tale unfolds, fate takes an unexpected turn, with even the male suitors pursuing Aria's love interests finding themselves enchanted by Kashumir, much to her chagrin. All Kashumir ever wanted was to defend her beloved sister.