The Female Knight is a central figure in the story. As her title suggests, she is a warrior of exceptional skill and a former companion of the Hero. She is a tall, strong woman with a freckled face, a feature she is notably self-conscious about. Like almost all characters in the series, she is never given a personal name, and is known only by her role.

In the past, the Female Knight traveled alongside the Hero and other companions. After the Hero disappeared following his fateful encounter with the Demon King, she settled in the Lake Nation, taking on the role of an abbess at a local church. It is during this time that the Hero, now allied with the Demon King in her guise as the Crimson Scholar, reunites with her to introduce new agricultural methods like the potato, seeking her help to spread these ideas and improve the human realm.

The Female Knight is defined by her unwavering loyalty and a fierce, principled dedication to the Hero. She has deep romantic feelings for him, which remain largely unrequited due to the Hero's singular focus on his grand mission. This creates a friendly but clear rivalry with the Demon King, who also loves the Hero. Despite this, her devotion is absolute; she formally offers him her sword, swearing eternal loyalty in a knighting ceremony. She is also incredibly self-conscious about her appearance, particularly her freckles and her more muscular, less traditionally delicate figure.

Her primary motivation is to serve and protect the Hero, as well as to fight for a better future for humanity. Believing in the Hero and the Crimson Scholar's vision of a peaceful, prosperous world without war, she dedicates her martial prowess to that cause. She is not driven by political ambition but by a sense of duty, love, and a desire to be useful. Her role in the story is that of a key military commander and a steadfast ally on the human front. While the Hero and Demon King operate on a grand, strategic level involving economics and politics, the Female Knight executes the military side of their plan. She is instrumental in the war effort, leading the armies of the Winter Kingdom into battle. Her most notable military achievements include leading the charge at Aurora Island and personally slaying the Arctic General, a powerful demon leader. In a high-stakes confrontation, she also volunteers to stop the Archbishop at the Tower of Light, defeating him in a struggle to prevent a catastrophic event.

Throughout the narrative, the Female Knight undergoes significant personal development. Initially, she struggles with being a woman in a male-dominated military world, facing prejudice and being ignored. However, once her status as a former companion of the legendary Hero becomes known, she gains the respect and acceptance of those she trains and leads. Her most profound moment of growth comes when the Crimson Scholar confesses her true identity as the Demon King. The Female Knight reveals that she already knew this secret, having been told by the Hero. She accepts the Demon King not as an enemy, but as a friend, choosing to believe in their shared goal of peace.

Her abilities are formidable. While her raw power is not on the same legendary scale as the Hero's, she is an incredibly strong and skilled warrior, capable of defeating a demon general in one-on-one combat. She is an accomplished commander on the battlefield, known for her tactical acumen. Furthermore, she is an excellent and systematic teacher of swordsmanship, able to instruct from the basics, which makes her more beneficial to learners than the instinct-driven Hero. She eventually learns the truth about her own past, as it is revealed she was once the princess of a fallen empire.