Celia Claire is the daughter of the Earl Claire household of the Beltrum Kingdom. She is hailed as the best genius magician in the Strahl Region of her era. Having skipped grades due to her talent, she graduated from the Beltram Royal Academy and became a lecturer at the royal institute at the age of only twelve. Despite her youth, she dedicates most of her time to researching magic, which has resulted in several magical inventions famous throughout the region.

Physically, Celia is a petite girl with a youthful appearance, often being mistaken for being younger than she actually is, much to her own chagrin. She has long silver hair that she typically ties into twin ponytails while letting the rest hang down her back. On occasions when she needs to disguise herself, she uses magic to change her hair color to blonde and ties it in a side ponytail.

Celia possesses a warm and kind personality, and she is known for not looking down on people of lower social standing, treating everyone with the same respect. She is a refined noble who enjoys tea and has particular preferences regarding it. However, when her interest is piqued as a researcher, she becomes oblivious to her surroundings and can remain cooped up in her laboratory for days. This intense focus comes with the side effect of making her rather disorganized, as she is bad at housework and keeps a messy room. She is also slightly introverted and has low stamina.

Her primary motivation stems from her passion for magical research and invention, but her personal life is deeply influenced by her bond with Rio. Initially, she is driven to help him learn and integrate into the academy. Later, her motivations shift towards seeking freedom from a forced political engagement and protecting those she cares about. After being forced into an engagement with Charles Arbor as his seventh wife to secure her talents for a political faction, Celia finds herself under house arrest. Her reunion with Rio, who comes to rescue her, marks a turning point, leading her to flee the kingdom and eventually become involved in larger political conflicts, including escorting a princess to safety.

In the story, Celia serves as a pivotal figure in Rio's early life, acting as his teacher and one of his first genuine friends within the noble society. She is a respected magic researcher and lecturer whose abilities make her a target for political manipulation. Her role evolves from an academic into a fugitive, a protector, and a key ally to both Rio and the royal family. After escaping the kingdom with Rio, she becomes a lecturer for the academy of the Restoration faction and an important figure in its political landscape.

Her most significant relationship is with Rio. She first met him in the slums and later became his homeroom teacher and personal tutor at the academy. Unlike other nobles, she treated him with kindness and respect, leading to a close friendship. Over time, she developed romantic feelings for him, though she tried to suppress them. When she was about to be forced into marriage, she realized the true depth of her feelings and asked Rio to take her away. She often gets annoyed when Rio interacts closely with other girls, particularly the spirit Aishia. With Princess Christina Beltrum, Celia shares a relationship of mutual respect, as Celia was her former teacher. She also becomes close friends with Aria Govaness during their school days, and later develops a good relationship with Rio's other companions, including Miharu Ayase, whom she lives with for a time and learns to cook from.

Throughout the series, Celia undergoes significant development. She starts as a sheltered academic genius but is thrust into a life of running and fighting due to political conspiracies. After being rescued by Rio, she learns to adapt to a new life outside the palace, gaining practical experience. She realizes her lack of combat skills and begins training in simulated battles. Furthermore, she learns to perceive magic power and gains fundamentals of spirit magic. At one point in her journey, she unlocks the ability to use ancient magic, and a powerful spirit notes that her high magical power may be due to having elf ancestry.

Celia is a notably powerful magician, considered the best of her era. Her magical skills are top-notch, allowing her to perform feats that surprise even seasoned fighters and city lords. In combat, she has demonstrated the ability to cast a variety of spells, including defensive magic to protect others and offensive spells like creating multiple earth lances, raining sharp icicles from a magical array, and summoning lightning strikes over a wide area. Her abilities are so potent that an antagonist considers her a significant threat after witnessing her activate a sage's magic.