Although she had been a promising practitioner of kendo in the past, due to an accident she was forced to lead a plain life. After Seo Yuri gets into a car accident during a trip back home, she reincarnates into the novel, *The Song of the Moon*, and becomes the elder twin sister of a side character who meets a destructive ending– Selena. Selena hopes to prevent the destruction of her family, however, she is forced to take the place of her runaway brother, Celestine, in the knights’ squadron! Will she be able to avoid the villainous Crown Prince, Ignis, and survive?! --- A lifetime as a fencing prodigy prepared Eunha for her new role as Selena Evan, novel side character and daughter of a renowned swordsman. Life isn't actually so bad after being sucked into a fictional world, but she’s doomed to meet an untimely death if she can't escape the clutches of the villainous Prince Ignus. When Selena's twin brother, Celestine, runs away before his military conscription, she has no choice but to enlist under his name to avoid getting her entire family executed. But hiding her identity won’t be so easy once Ignus takes note of her impressive sword skills and sets his sights on turning "Sir Celestine" into his top henchman. With the threat of execution looming over her head, can Selena avoid getting caught by the villain?