Ficelle Harbeller is a young woman who serves as a prominent supporting character in the story. She is a prodigy recognized for her mastery of both swordsmanship and sorcery, making her a rare and powerful magic swordswoman who is considered the ace of her magical squadron. In terms of appearance, she has black hair cut to the length of her shoulders and red eyes, and she typically wears the uniform of the Magic Corps.

Ficelle’s background is deeply rooted in her training under two exceptional masters. She first learned swordsmanship at the rural dojo of the master swordsman Beryl Gardinant, where she began as a young student from the countryside. After demonstrating her innate talents, she was also trained in magic arts by Lucy Diamond, a powerful wizard who leads the magic corps and directs a prominent academy. This unique dual education allowed her to combine both disciplines, creating a formidable fighting style that sets her apart as the only person currently capable of effectively using sword magic in real combat situations.

Her personality is defined by a strong work ethic and a serious, devoted nature. From a young age, Ficelle was praised by her parents and peers as a natural genius. However, the compliment that meant the most to her came from her swordsmanship master, Beryl, who praised her not for her innate talent but for her persistent effort. This experience shaped her core philosophy: she values hard work and perseverance above natural ability. She holds herself to an incredibly high standard, famously practicing a thousand sword swings every day, and she expects the same level of commitment from those she teaches. This dedication, however, makes her a somewhat difficult and clumsy teacher, as she tends to demand that all students match her own intense work ethic without necessarily having the same capacity for it. Despite her strict exterior, she has a desire for recognition and affection; after periods of intense exertion, she is known to seek out praise and enjoys being patted on the head by her companions. She typically speaks in a calm, measured way and uses polite, formal language when addressing her seniors. She also has a playful side and enjoys teasing her master, Beryl, in a friendly manner.

In the narrative, Ficelle plays several key roles. She is an instructor at the magic academy, where she teaches sword magic. Her position as a young teacher is a significant responsibility that connects her more closely with her own mentors. She is also a loyal member of Lucy Diamond's magic corps, often serving as a personal attendant and bodyguard to Lucy, who remains both her magic teacher and superior. The story explores her development, particularly regarding her teaching methods. When her overly demanding style proves ineffective at the academy, her former master, Beryl, is invited to observe and help her improve. By watching Beryl, who instructs students with praise and encouragement while still focusing on fundamentals, Ficelle is reminded of her own time as a student and begins to develop a more balanced approach to teaching.

Ficelle maintains several important relationships. She has a profound respect and loyalty for Beryl Gardinant, who was her swordsmanship teacher. She loves him not only as a master but also as a person, and she is deeply affected by his recognition of her hard work. She holds Lucy Diamond in equally high regard, and the two share a close bond, with Lucy actively encouraging Ficelle's career. Among her peers, she is closest to Curuni Crueciel, a fellow student of Beryl's, with whom she shares a strong sense of camaraderie and is able to fight in perfect sync despite belonging to different factions. Other disciples of Beryl, such as Allucia Citrus and Surena Lysandra, are considered her senior disciple sisters. She also becomes a tutor to Mewi Freya, a younger student, and has a firm but fair relationship with her, pushing her student through strict training while being happy to offer help when needed.

Regarding her abilities, Ficelle is an exceptionally powerful magic swordswoman. She has integrated her training in swordsmanship with her magical studies to develop the practice known as spellblade. This skill allows her to perform a variety of feats, such as launching magical shockwaves from her blade, enhancing her physical attacks with elemental magic, and even controlling her sword remotely through telekinesis. Her combat prowess is demonstrated in a notable fight against a church knight named Uro, who possessed a greater amount of magic power. Despite being at a disadvantage and affected by a debilitating spell, Ficelle was able to win the battle through her superior technique and control over her unique sword magic style.