Ruil was born 77 years ago in the fifth age to Iŝius and Haelienne. As her appearance and lack of magical affinities were apparent, she was born into the Ikudo caste as a warrior. Favored by her father, Ruil was raised to be his successor and thus became a skilled sword fighter by the time she was four. Despite the favoritism her sister faced from their mother, Ruil never resented her sister. When Erim was crowned King, Ruil decided to be her sister's protector and bodyguard, much to the astonishment of her father. Ruil set aside her own convictions for the greater good, and to protect the sister she loves.
Ruil is the sister of Erim, and greatly resembles her sister, other than her more muscular build, crimson red hair, and her own choice to use war paint, and the fact her body tattoos display lotuses, not bauhina. Ruil displays a confident, casual and friendly demeanor towards most people, especially those she respects for their fighting skills. She speaks with a very casual register, calling her sister "Sis" even in formal settings and lacking her sister's characteristic refinement of speech and appearance. However, Ruil is far from unintelligent and shows herself to be incredibly perceptive of those around her. Ruil often takes on the appearance and mannerisms of Erim for times where Erim must be away from the castle, and is more than capable of ruling in her sisters' stead. Her primary measure of someone's status is their fighting or battle tactics prowess, and her complete lack of a magical affinity leads her to put more effort into technique and skills.