Originally named Emerald Queen, she was heir to the Emerald Kingdom. Her parents perished in a fire set by an unknown traitor (Professor Clover in the anime), leading Silver Heart to rescue her. He concealed her origins, adopting her as his granddaughter. Raised alongside Joker and Spade at the Phantom Thief Academy, she graduated as a professional phantom thief.

Initially an antagonist, Professor Clover manipulated her into believing Silver Heart murdered her parents. This drove her to attack Silver Heart, severely injuring him, and destroy treasures including Morrighan's Silver Plate and the Silver Wolf Bust. After Joker exposed Clover's deception, she reconciled with Silver Heart and allied with Joker and Spade.

She possesses long blonde hair in pigtails, golden eyes with diamond-shaped pupils, and a diamond-shaped birthmark on her right hand. Her outfit features a white bodice with fuchsia details, a short mantle, a wrap skirt, knee-length boots, and a diamond necklace from Silver Heart. Her manga design later evolved to match the anime.

Energetic, cheerful, and strong-willed, she adores jewelry but avoids chores. Her clumsiness in cleaning and cooking requires help from her companion, Roko, a genetically modified dog who speaks and emits destructive sound waves. Roko serves as her primary assistant in the anime (the manga featured a different assistant). She relies on brute strength and her "absurdly sharp" diamond sword, capable of cutting nearly anything, rather than gadgets.

Later, she collaborated with Joker and Spade on heists, like stealing the Rainbow Peacock Egg where her gluttony caused temporary weight gain. In the sequel manga *Kaitou Shounen Jokers*, she married Joker, bearing a son training as a phantom thief and an unnamed infant daughter. She disappeared before the events of that story.