Maron Kusakabe is the main protagonist of the series. She is a sixteen-year-old high school student who appears to be an ordinary girl, though she is exceptionally talented in gymnastics. She lives alone in an apartment because her parents moved overseas for work when she was young and later separated. This abandonment has left her with deep feelings of loneliness, which she conceals behind a cheerful and warm smile. She is well-liked at school but keeps others at a distance, struggling with trust issues and a cynical view of love, believing that people can fall out of love as easily as they fall into it.

Maron is chosen by God to be the reincarnation of Jeanne d'Arc and is given a mission by the angel Finn Fish. Her task is to seal away demons that have come to Earth and are hiding inside objects of great beauty, such as paintings and artwork, where they feed on the purity and beauty in human hearts. By transforming into Kaitou Jeanne, the phantom thief alter ego, she uses a special pushpin to strike the demons and capture them by shouting Checkmate, which turns them into chess pieces. Because the artwork disappears after she seals the demon, she is perceived as a thief by the outside world. As Kaitou Jeanne, she can fully utilize her gymnastics abilities for agile movement and acrobatics, and she wields a baton ribbon and a fan in combat.

Her primary motivation is fulfilling this divine mission to prevent God's power from waning and to protect humanity. Underneath this duty, however, her journey is driven by a deeper, personal need to confront her own insecurities, overcome her fear of abandonment, and find genuine emotional connections. Maron is stubborn and strong-willed, but she is also deeply kind and compassionate, always putting the needs of others before her own. Her emotional growth is a central part of the story. After a devastating betrayal leaves her unable to transform into Jeanne, her soul travels back in time to fifteenth-century France, where she meets the real Jeanne d'Arc. In this crucial moment, she finds the courage to inspire Jeanne and reclaim her own power, leading to a new transformation and a more assertive fighting style that includes a sword. From that point, she learns to rely on her own strength even without her magical form.

Maron's closest relationship is with her best friend and neighbor Miyako, who is the daughter of a police detective tasked with capturing the phantom thief. Despite the secret that hangs between them, Miyako provides Maron with a sense of family and belonging. Another key relationship is with Chiaki, a new classmate who initially knows her identity as Jeanne and approaches her with the intention of stopping her collection of chess pieces. Maron begins by hating Chiaki, but as he persistently pursues her and she learns his true nature, she slowly falls in love with him. Through Chiaki, she learns that it is acceptable to cry and to lean on others for support. Her relationship with Finn, the angel who guides her, is central to her role; Finn provides her with power and purpose, and the bond between them is one of mutual care and reliance. In the manga, Maron eventually marries Chiaki, and they have a daughter named Natsuki, representing the family and emotional fulfillment she long desired.