Elfine Phillet is a seventeen-year-old student at Excalibur Academy and a member of the eighteenth platoon, serving as its communications and support specialist. She is depicted as a beautiful young woman with long, sleek black hair that reaches her hips, which she often wears with braids on each side secured by green hair bobbles and an orange clip. Her eyes are purple, and she typically wears the standard female uniform of the academy.

In terms of personality, Elfine presents a cheerful and kind demeanor, making her approachable and friendly to her comrades. Despite her warmth, she also possesses a strict side and has a strong commitment to following the rules of the academy. She does not tolerate those who break regulations and is willing to report such infractions to the authorities for proper punishment. This strict adherence to rules was notably demonstrated when she threatened another student, Muselle Rhodes, for his inappropriate behavior.

Elfine's role and motivations are profoundly shaped by events in her past. Originally, she was the leader of the seventh platoon and an attacker on the front lines, specializing in firepower. However, during a mission to investigate ruins six months prior to the main story, her unit fell into a trap set by the Void, the primary antagonists of the series. While Elfine survived, two of her colleagues perished. This traumatic event left her deeply burdened by survivor's guilt, causing her to lose much of the power of her Holy Sword. Consequently, she withdrew from active combat duty. It was Riselia Ray Crystalia, the leader of the eighteenth platoon, who persistently reached out to Elfine and persuaded her to return to duty, though in a support capacity as the platoon's operator. Beyond her immediate trauma, Elfine is also driven by a desire for revenge against her own father, Dimphlord Phillet, who she believes killed her mother in a cruel human experiment.

Her key relationships are central to her character development. She holds deep respect and gratitude for Riselia, who helped her during her lowest point and recruited her into the eighteenth platoon. With Leonis, the protagonist, she is initially welcoming, even allowing him to stay in the girls' dormitory against the rules. As she observes his extraordinary abilities, she becomes curious about his true identity but ultimately places her full trust in him. She also becomes aware of his particular interest in her physique, though she deeply appreciates him for being instrumental in restoring her self-confidence, which in turn helps her regain control over her powers. Her family relationships are complicated; she is on poor terms with her older sister, Clauvia Phillet, whom she distrusts and has labeled a malicious witch. This suspicion likely stems from Clauvia's alignment with their father or involvement in his questionable research.

Throughout the story, Elfine undergoes significant personal development. Struggling with the guilt and trauma of losing her former platoon, she can initially only use a fraction of her Holy Sword, the Eye of the Witch (also known as the Celestial Orb), limiting her to basic reconnaissance and communication functions. Her primary ability is related to analysis and commentary, effectively serving as the team's eyes from a support position. However, through her experiences with the eighteenth platoon and the encouragement of Leonis, she begins to recover her former strength. A pivotal moment occurs when she regains the ability to access her Holy Sword's true battle form, known as the Ray of Vorpal (or Demon Lightning), allowing her to once again fight as an attacker. This reclamation of her power symbolizes her overcoming her past trauma. Later in the series, her journey takes a darker turn when she becomes corrupted by the darkness of a demon sword, though she is eventually rescued from this state.