Agnès Chevalier de Milan is the captain of the Royal Musketeer Knights, an elite all-female unit that protects Queen Henrietta of Tristain and carries out vital missions. She survived the destruction of her village, D’Angleterre, which was burned by fire mages under the false pretense of containing a plague, an event that killed her parents and left her as the sole survivor. This trauma instilled in her a deep distrust of magic users, particularly fire mages. Despite her commoner origins, she was granted a title and position by Queen Henrietta, to whom she is fiercely loyal.

Driven by a quest for vengeance, she initially targeted a man named Lishman as the perpetrator and killed him during a mission. Later, she learned that the true leader behind the burning was Jean Colbert, an academy teacher known as “Flame Snake.” When she attempted to kill Colbert, she recognized him as the stranger who had saved her from the fire years before. Although consumed by hatred, she chose not to kill him, recognizing that perpetuating violence would harm his students. She vowed never to forgive him but later provided troops for his mission to rescue Tabitha, committing to end the cycle of hatred.

Agnès trains students at the Tristain Academy of Magic in non-magical combat, stressing that mages should not rely solely on magic. She mentors Saito after he loses his Gandálfr powers, teaching him swordsmanship to protect Louise. She is a master swordswoman and firearms specialist. Physically, she has dark blonde hair and cyan eyes, and typically wears military attire including capes, thigh-high boots, and fingerless gloves. Her demeanor is disciplined and stern, though she occasionally shows openness around trusted individuals like Henrietta and Saito. Rumors about her sexuality exist, though they lack supporting evidence.