Kuroizeru, also known as Croyzel, is an insectoid-like robotic monster that serves the Crisis Empire in Kamen Rider BLACK RX. It possesses the ability to manipulate heat by harnessing energy from the sun. The Crisis Empire dispatched Kuroizeru to create a severe heat wave in the city using an artificial sun, as part of a scheme to capture a scientist. It was deployed alongside the foot soldiers known as Chaps and the Skullmastars. Visually, it resembles a mechanical insectoid. Beyond its role as a heat-manipulating weapon of the Crisis Empire, no further details about its personality, internal motivations, or any developmental arc are known; it functions as an episodic threat. Its key relationship is its position as a subordinate within the Crisis Empire's forces, acting under the command of higher-ranked villains.