Jeanne dArc is a central character in Fate/Apocrypha, where she is summoned by the Holy Grail itself to serve as the Ruler-class administrator for an abnormal conflict known as the Great Holy Grail War. Unlike ordinary Servants who fight for a Master and a personal wish, a Ruler is a neutral arbiter with the sole duty of ensuring the Holy Grail War proceeds correctly, though in this case, the situation forces her to take a more active role. She is the famous Maid of Orleans, a French heroine and Catholic saint who led her nation to key victories during the Hundred Years' War before being burned at the stake as a martyr. As a Heroic Spirit summoned without a personal wish on the Grail, she carries no regrets about her life and views her martyrdom as a final choice made of her own free will.

Physically, Jeanne manifests using the body of a French village girl named Reticia, a pseudo-Servant arrangement made with the young woman's consent. This unique situation means Jeanne cannot shift into spirit form and must eat and sleep to maintain her vessel, though she retains all the superhuman physical abilities of a Servant. She stands 159 centimeters tall and possesses a slender build, with long blonde hair typically worn in a practical braid. Her outfit combines a simple commoner's dress with pieces of armor on her arms, torso, and legs, along with a headpiece, allowing for both mobility and protection. Her primary armament is not a sword but a holy flag she carries into battle, reflecting the historical account that she commanded using her banner rather than directly killing enemies.

Jeanne's personality is defined by profound humility, compassion, and an unwavering commitment to her faith. Though widely revered as a saint, she consistently rejects such titles, insisting she is simply a woman who answered God's call and is unworthy of special veneration. She is aware of the moral complexity of her actions in life, acknowledging that her hands were stained with blood the moment she took up her flag to lead armies into war. When acting in her capacity as Ruler, she often appears calm, taciturn, and strictly impartial, but her genuine nature is that of a simple, gentle, and somewhat naive sixteen-year-old girl. She possesses a remarkable capacity for empathy, praying even for her enemies and showing deep compassion toward suffering souls. This is most powerfully demonstrated during her encounter with the Servant Jack the Ripper, where she recognizes the entity as a composite of lost and abandoned children's souls and uses her abilities to grant them peace rather than simply destroying them in anger.

Throughout Fate/Apocrypha, Jeanne's primary motivation shifts from acting as a detached arbiter to protecting a young homunculus named Sieg. After the homunculus is saved by the sacrifice of the Black Saber, Siegfried, Jeanne discovers him and feels a strong sense of responsibility for his wellbeing. She acts as his guardian and mentor, initially urging him to stay away from the violent conflict so he can experience the joys of living a full life. However, as Sieg inevitably becomes drawn into the Grail War, Jeanne resolves to stand by his side and ensure no harm comes to him, forming the story's most significant relationship. This bond deepens over the course of the narrative, with Jeanne and Sieg developing a strong mutual affection that can be described as romantic. Her other key relationships include her role as a rival to Amakusa Shirou Tokisada, the Ruler from a previous Holy Grail War who serves as the primary antagonist and seeks to use the Great Grail for his own plan to grant humanity immortality, a goal Jeanne believes transgresses the natural order and the will of God. Throughout the conflict, she also allies with several Servants, including the Red Saber, Mordred, and the Rider of Black, Astolfo.

As a Ruler-class Servant, Jeanne possesses several exceptional abilities granted specifically for her role as an administrator. She can automatically discern the true name, skills, and parameters of any Servant she encounters, and she can detect all Servants within a ten-kilometer radius, rendering an Assassin's presence concealment useless against her. Her command over the war is absolute in theory, as she holds two Command Spells for each of the fourteen participating Servants, giving her significant authority to enforce the rules. Her personal combat abilities focus heavily on defense and divine protection. Her first Noble Phantasm, Luminosité Eternelle, meaning God is with me, allows her to plant her holy flag and create a powerful defensive barrier that negates incoming attacks for herself and those near her, a manifestation of the divine protection she received during her lifetime.

Jeanne's ultimate ability is her second Noble Phantasm, La Pucelle, also known as the Crimson Holy Virgin. This is a suicidal attack of tremendous power that crystallizes the concept of her death by fire into a conceptual weapon. To activate it, Jeanne draws the Sword of Saint Catherine, a blade she never once swung in life, and recites verses from Psalm 19 before declaring her devotion to the Lord. As the incantation completes, the sword's hilt blossoms into a rose, and divine flames erupt from it, recreating the fire of her martyrdom as a holy inferno capable of annihilating anything she deems necessary to destroy. This power can only be used out of a genuine desire to save something or someone; it cannot be invoked from hatred, vengeance, or mere battle lust. As a suicidal Noble Phantasm, using La Pucelle means Jeanne will disappear after the battle, giving her life a final time to protect the future of humanity from Amakusa's plan. Her willingness to sacrifice herself in this manner reflects the core of her character: a saint who gave everything in life and is prepared to do so again, not out of a desire for glory, but from a quiet, unshakable conviction in her sacred duty and her compassion for others.