Millie Maxwell is a researcher who works for the Clover Kingdom’s 0th branch of the Magic Tool Research Lab. She first appears in the film Black Clover: Sword of the Wizard King. Physically, she is a slender woman with medium-length, wavy green hair that she pulls back with a red headband. Her role in the story is that of a behind‑the‑scenes support figure rather than a frontline combatant. She coordinates research and development of magical tools, often working alongside the eccentric scientist Sally. Millie is cautious and methodical by nature; she dislikes entering a situation without a well‑thought‑out plan. This careful approach shapes her primary motivation, which is to contribute meaningfully to the kingdom’s defense by creating effective tools and weapons. In the film’s narrative, she provides the Magic Knights with essential equipment that aids them against the revived former Wizard Kings. Her key professional relationship is with Sally, with whom she collaborates closely on experiments and inventions. The film establishes her as a dedicated researcher, and later, in the ongoing manga, her character is integrated into the main canon. During the final battle against Lucius Zogratis, Millie and her research team develop a special type of ammunition that temporarily disables an enemy’s ability to use magic for five seconds. This invention allows allies to capitalize on brief windows of vulnerability. While she does not possess remarkable personal combat magic, her strength lies in her analytical mind and her expertise in magical tool engineering. Her development is subtle, moving from a background role in the film to a more active contributor during the kingdom’s most desperate hour.