Millerna Sara Aston is the third princess of the kingdom of Asturia, the youngest daughter of King Grava Aston and Queen Therese Aston. She has two older sisters: Marlene, who is deceased and was the wife of Duke Freid and the mother of Allen Schezar’s son, Chid; and Eries, who pressured Millerna to abandon her medical studies. Millerna’s early ambition was to become a doctor, a pursuit she was forced to give up due to her sister’s interference. Despite her royal status, she is intelligent, compassionate, and independent, possessing a strong will and a tendency to push back against tradition and the burdens placed on her as a princess. Her personality is polite and well-mannered, yet she can be stubborn and even somewhat tomboyish. She is unafraid to follow her passions, which leads her to run away from Asturia to join Prince Van’s group in order to fulfill her dreams and stand against the Zaibach Empire.

Millerna is deeply in love with the knight Allen Schezar, though he does not reciprocate her romantic feelings. She is betrothed to the merchant prince Dryden Fassa, a match she initially resents. Over time, she gradually comes to appreciate Dryden’s good qualities and genuine care for her. At the end of the series, they part on good terms, with Dryden promising to return when he feels more deserving of her. This experience leads Millerna to realize that she cannot rely on others to make her happy. Her role in the story is that of a supporting character who provides medical expertise, notably performing surgery on Allen when he is injured and helping him rehabilitate. She also becomes a close companion to Hitomi Kanzaki, despite initial jealousy over Allen’s attention toward Hitomi. Millerna’s development moves her from a lovesick, dependent princess to a more self-reliant individual who takes charge of her own path. Her notable abilities include her medical knowledge and surgical skills, which she uses to aid the group throughout their journey.