Youko was 16 years old in Japan, where she studied as an honor student. Her main concern was her naturally red hair. One day at school, Keiki appeared suddenly and bowed before her, pledging his loyalty. Then, a giant bird attacked the school, prompting Youko to reluctantly accept Keiki's protection. He gave her a sword and transported her along with two classmates to Kou's kingdom.
She eventually learned that she was the heir to the throne of the kingdom of Kei, and although she was initially reluctant, she accepted the position through her growth in the story. Among the obstacles she faced were the king of Kou, who used her classmate Sugimoto in his effort to stop her from attaining the throne. In a later story arc, as the newly appointed queen, Youko learned of several problems in her kingdom, including a revolt in the province of Wa.
Despite being a weak character to begin with, appearing very withdrawn and not wanting to do anything that would bring attention to herself; Youko eventually grows throughout the episodes (especially seen in episode 5). She grows in strength and maturity, becomes empathetic towards the people around her, thinking articulately about her actions (especially as queen) and continues to do so through towards the end of the series.
Her nickname is "Sekishi" ("red child"), after her bright red hair.