Queen once trained as a phantom thief with Joker and Spade under the tutelage of Silver Heart, but she now works for Professor Clover. She holds a grudge against phantom thieves and goes around destroying treasures so nobody else can steal them. Her assistant and closest companion is a talking dog named Roku, and her primary weapon is a diamond-bladed sword.
Queen’s parents ruled the Duchy of Emerald, until Professor Clover killed them when she was an infant. Silver Heart took her from the castle at the request of Queen’s dying mother, and raised her as his granddaughter. To protect her from assassination attempts, he kept her lineage a secret. Years later she learned her true identity from Professor Clover, who also manipulated her into thinking Silver Heart killed her parents and kidnapped her. She abandoned her training and swore revenge against Silver Heart and all other phantom thieves.
Queen eventually reconciles with Silver Heart and her childhood friends Joker and Spade, after Joker finally tells her the full story of how Silver Heart adopted her and why he kept her identity hidden. After that, she completes her training and becomes a full-fledged phantom thief.