Etoile, whose real name is Estelle, is a young soldier from the kingdom of Lusitania and a secondary character in the story. She is approximately the same age as Prince Arslan and serves as a page under Lord Guiscard, the younger brother of the Lusitanian king. To navigate the male-dominated military environment, she adopts the alias Etoile and conceals her gender, presenting herself as a boy. Physically, she has short, messy blonde hair and caramel-colored eyes.

Etoile is defined by her tough, stubborn, and brash personality. She is a fervent believer in the Lusitanian religion of Yaldabaoth and initially holds deep-seated prejudice against the people of Pars, whom she considers heathens. Her religious conviction is so strong that she is gullible enough to believe outlandish rumors about Prince Arslan, such as the claim that he has horns. Despite her hot-headedness and the harsh front she presents as a soldier, she possesses a good-mannered and kind nature compared to other Lusitanians. She is uneasy around women, having lived her life disguised as a male, and dislikes being reminded of her gender as she feels it would cause others to look down on her.

Her personal motivations are rooted in both faith and friendship. After being taken as a prisoner of war following an earlier conflict, she escaped and later joined the Lusitanian forces, partly in search of her friends who were enslaved alongside her. She eventually learns from Arslan that those friends were killed.

Etoile's primary role in the story is as a mirror and a foil to Arslan. Their fates become intertwined after she kidnaps him, mistaking the prince for the pampered son of a noble family. Throughout the series, their repeated encounters serve as a continuous process of education for both characters. While Arslan is pushed to move beyond his naivety and understand the cruelties of the world, Etoile is forced to confront her own prejudice and the extremist teachings of her nation. She initially dismisses Arslan's claims that Lusitanian leaders exploit their religion for greed, but after becoming entangled in Guiscard's political conspiracies and assassination attempts, she begins to accept the truth of his words and understand the wrongdoings of her country.

The relationship between Etoile and Arslan is complex and central to her character. Despite her belief that he is a heretic, she gives him a Lusitanian Bible and tells him she would welcome him to the castle if he converts. During a covert mission where she poses as a maiden, Arslan does not recognize her but helps her escape from danger. In a pivotal conversation, Arslan explains his desire to help the country of Pars, which makes Etoile begin having second thoughts about her blind hatred. Her care for Arslan becomes evident when she warns him not to lose his life in the war and prays for his safety, effectively deciding not to fight him in the future. As events unfold, she finds herself used as a pawn by her own leaders, yet she actively seeks out Arslan, recognizing him as someone she trusts implicitly even as she rejects his faith.

In terms of abilities, Etoile is a capable and trained soldier of Lusitania. She holds the rank of a page and leads a squadron of soldiers, demonstrating her competence in combat and leadership. She is proficient with standard military equipment, including chain mail cloaks and metal helmets, and has been shown fighting on the battlefield during major conflicts such as the battle for the Keep of Saint-Emmanuel. Her most notable abilities, however, may be her resilience and her capacity for moral growth, as she evolves from a rigid, ideologically driven soldier into a character who can question her own nation and form a bond with a person she was raised to see as an enemy.