Nagisa Misumi is a teenage girl who serves as one of the two main protagonists of the Pretty Cure series. She is a student at Verone Academy, where she is a second-year and later third-year student, and she is the ace player of the school's lacrosse team. Nagisa is energetic, outgoing, and passionate about sports and food, but she struggles with academics and dislikes studying. Her enthusiasm for life is matched by a strong sense of justice, though she can be reckless at times. Despite her athletic and tomboyish exterior, Nagisa has a very girlish side: she dreams of romantic love, is image-conscious, collects stuffed animals, enjoys shopping, and loves sweets, especially chocolate and foods with the word "yaki" in their names. She is popular with her female classmates, who find her cool and princely, but she is frustrated that she does not attract the boys she likes. She has a crush on an older boy named Shougo Fujimura, often called Fuji-pi, and becomes flustered around him.

Nagisa's life changes when she encounters a small fairy named Mepple, who comes from the Garden of Light. She becomes Mepple's caretaker and gains the ability to transform into the magical warrior Cure Black, the "emissary of light." Her transformation device is the Card Commune, and she uses a Queen Card to activate it. As Cure Black, she possesses superhuman strength, agility, and endurance, and she is the physically stronger half of the Pretty Cure duo. Her signature attack is the Marble Screw, which she performs while holding hands with her partner, Cure White. This combined technique also grants them lightning-based powers. Nagisa's athletic background—especially her lacrosse skills—translates directly into her fighting style, and she can even use her lacrosse stick as an improvised weapon.

At the beginning of the series, Nagisa is reluctant to accept her role as a Pretty Cure and initially clashes with her partner, Honoka Yukishiro (Cure White), who is more reserved and studious. Over time, the two overcome their differences and develop a deep, inseparable friendship. Nagisa becomes fiercely protective of Honoka, Mepple, and later their ally Hikari Kujou (Shiny Luminous). Her motivations grow from a sense of duty to a genuine desire to protect the people she cares about and the world from the forces of the Dark Zone. Nagisa also has a younger brother named Ryouta, with whom she often argues, but she is protective of him as an older sister.

Throughout the series, Nagisa matures from a somewhat self-centered and impulsive girl into a responsible and dependable hero. She learns to balance her personal desires with her responsibilities, and her bond with Honoka becomes the emotional core of the story. Her notable abilities include her natural athletic prowess, her super strength as Cure Black, and her capacity for powerful dual attacks with Cure White, such as the Marble Screw, Rainbow Therapy, and later the Marble Screw Max in the sequel series. Her catchphrase is "Unbelievable!" reflecting her expressive and dramatic personality.