The Zetsumerise Key is a special device used in the world of the *Kamen Rider* franchise, particularly in the series *Kamen Rider Zero-One*. It serves as a transformation tool that allows characters to access various powers and abilities. Each key is associated with a specific *Zetsumerise* animal or object, enabling the user to harness unique skills during battles. In the series, the Zetsumerise Key is often used in conjunction with the *Zetsumerise Driver*, which is the main transformation belt. The keys can be collected and exchanged, adding a collectible aspect to the storyline. This feature enhances the dynamic nature of the battles and character development within the *Kamen Rider* universe.