Maron is 16 and a seemingly ordinary high school student. She is extremely gifted in gymnastics. Her alter-ego is Kaitou Jeanne (phantom thief Jeanne), the reincarnation of Jeanne D'Arc. Through the angel Finn, who is sent to help her, she receives a mission from God to seal away demons who have come to Earth to steal the beauty in human hearts. The demons, which are hidden inside objects of great beauty (usually pieces of artwork) are captured when Jeanne hits them with a pushpin and shouts "Checkmate!", turning them into chess pieces. She is a lonely character who hides her feelings behind a warm smile.
At a very young age her parents left her for their jobs over seas, and have not contacted her since then. The first phone call she gets is from her mother, informing her that they have have decided to get a divorce. As a result, she lives alone, although is very close with the family of her best friend and neighbor Miyako. She starts out hating Chiaki when they first meet, but falls in love with him as they become closer and the series progresses. She marries Chiaki in the manga, and they have a daughter named Natsuki (the reborn form of Finn or the past life of Finn (manga).