Zeros made their debut alongside Kihunters in Super Metroid, appearing in numerous areas of Planet Zebes. It was not until Metroid Fusion that it became clear that Zeros are larval Kihunters, with their metamorphic life cycle displayed over the course of the game. In Metroid: Other M (the source of their Smash design), Zeros were cloned aboard the Bottle Ship, where they could be found in the nest of a King Kihunter in the Biosphere.
Zeros, along with FG II-Graham units and Joulions, appear as stage hazards on Pyrosphere. The weighty Zeros drop down onto the stage and then crawl slowly on the floor. If picked up by a fighter, their weight makes the fighter more difficult to launch. They can also be thrown at opponents or at Ridley to inflict damage.