Hiden's Zetsumerise Keys are special devices used in the Kamen Rider Revice series. They allow the user to access various powers and abilities by unlocking different forms. Each key is designed to represent a specific Kaijin or monster, enabling the user to transform and gain unique skills. These keys are essential for the main characters, particularly Ikki Igarashi and Daiji Igarashi, as they battle against the forces of evil. The Zetsumerise Keys play a crucial role in the storyline, providing both challenges and advantages in their fight against the Deadmans.