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?!

Once upon a time, there was a leak in the sky and the residents of the sky kingdom sneaked out to the human world. They were known as monsters and gods because they are totally different species. One day, five Ahrangs came to earth by God's will in order to send the sky people back to where they belong. After ever-lasting battles, the sky people were finally gone and never seen again by the world. However, it's rumoured that the legendary Ahrangs remained in the land still in search for sky people.