Grey is a Magic Knight of the Clover Kingdom belonging to the Black Bull squad. Her real name is unknown, and she is a commoner by birth. Her early life was marked by hardship; after her father remarried, she was mistreated by her stepmother and two elder stepsisters, forced to perform all the household chores. In an attempt to gain their acceptance after receiving her grimoire, she used her magic to transform and look more like her stepsisters. This act backfired, as they reacted with outrage and chased her from her home. While wandering alone, three men attempted to rob her, but she was saved by Gauche Adlai, who told her she must be prepared to do everything for herself if she chose to run away.

Grey is defined by her extreme shyness in her true form, becoming easily flustered and embarrassed. She typically hides her real appearance, suffering from a deep lack of confidence born from the years of verbal and physical abuse from her stepfamily. When she uses her magic to transform into someone else, her personality shifts dramatically. While disguised, she becomes friendly, outgoing, and enjoys cooperating with her squad mates. She demonstrates impressive observational and acting skills by imitating the attitudes and mannerisms of the person she has transformed into. Beneath her shy exterior, she is incredibly kind-hearted, though also somewhat naive, as shown by her lingering hope to mend her broken family relationships despite their cruelty.

Her primary motivation is to overcome her deep-seated embarrassment and insecurity regarding her true self. Her initial reason for constantly using her transformation magic was to hide her identity from others, including her fellow Black Bulls. Over time, as she bonds with the squad and experiences their acceptance, she develops a desire to face her fears and stop hiding. She is also driven by a sense of loyalty and gratitude, particularly toward Gauche, whose encouragement gave her the resolve to live independently and who continues to be a key figure in her life. She fights to protect her new family in the Black Bulls and proves her courage in critical moments, refusing to give up when their base is attacked.

The key relationship in Grey's life is with Gauche Adlai. He saved her from robbers after she was exiled from her home, and she later joined the same Magic Knight squad as him. She harbors deep feelings of indebtedness to him, and his advice and observations during battles directly contribute to her discovering new facets of her magical abilities. The flashbacks to their first meeting reveal the profound impact he had on her. She shares a bond with her other squad mates in the Black Bulls, a group of misfits who ultimately accept her for who she is. This acceptance is a crucial factor in her character development, as the supportive environment contrasts sharply with her traumatic childhood.

Grey undergoes significant development throughout the story. For a long time, even her fellow squad members did not know her true appearance, as she was always disguised, often as a giant, faceless figure. A major turning point occurs during the Seabed Temple arc. After she exhausts her mana and her disguise fails, her true form as a blue-haired young woman is revealed to Gauche and Charmy. Despite her extreme embarrassment, this event marks the beginning of her journey to be more open and not hide her face from her comrades. Later, when Gauche is critically injured, her desperate wish to save him unlocks a new level of her power, revealing that her magic is far more complex and potent than simple transformation. She learns to use her abilities to heal fatal wounds by transmuting the damaged matter itself.

Grey's notable abilities center on her unique magic. On the surface, she uses Transformation Magic to alter her own appearance, taking the form of other people, including her squad mates or a large, intimidating man. However, her true power is an incredibly rare and powerful form of Transmutation Magic. This allows her not only to change the appearance of objects but to fundamentally disassemble and reassemble materials, converting one substance into another. She can transmute a rock into food, poison into cotton, or enemy spells into a different elemental attribute, a technique known as Magic Convert. Because of this ability to alter non-magical substances and other magic itself, Grey is classified as an Arcane Stage mage. She can also use this transmutation ability to heal grievous injuries by converting damaged tissue back into a healthy state. While she lacks conventional offensive spells, her support capabilities are considered immensely valuable.