Chase was one of the main characters in the series, Kamen Rider Drive. For a short time, Chase was the original Kamen Rider of the series, Kamen Rider Proto-Drive as called by Krim Steinbelt himself prior to the event that would later be known as the Global Freeze.
At this point in time, Drive was not fully operational and completely rendered Chase to only being capable of destroying a Roidmude’s body rather than destroying them entirely. Sometime during the Global Freeze, Chase was incapacitated by Heart and was robbed of his memories.
Reborn with a new purpose, he was given equipment that was based on the original Drive’s equipment using Viral Cores in place of Shift Cars allowing him to assume the form Roidmudes call Mashin Chaser (Advance Demon Chaser). In this form, he is able to rival the current Drive, Shinnosuke Tomari and with the ability to augment additional Viral Cores, he can fight evenly against the second Drive’s additional forms granted by the Shift Cars.
As an enforcer sent by Heart and Brain to police the lower Roidmudes by destroying their bodies if they get out of line, Chase is notoriously known as the Grim Reaper, a name he dislikes due to the fact he never killed for good any Roidmude, unlike Drive, who he considers a true Grim Reaper.
In truth, Chase is either a rejected Roidmude or the prototype of the modern Roidmudes and is classified as Proto-Zero and is a Human-Type Roidmude.
He regains his memories in the future and becomes Kamen Rider Chaser!