Mezool is a Greeed and one of the main antagonists in Kamen Rider OOO. She is associated with the aquatic Core Medals and is characterized by her elegant yet cold personality, often acting with a regal, manipulative demeanor. Mezool plays a major role in the conflict over the Core Medals, working alongside the other Greeed to restore their full power. Her actions drive many of the series' early confrontations and highlight the danger posed by the Greeed to humans.