Shiro Kazami was a college student majoring in biochemistry before he witnessed the murder of a man at the hands of an agent of the Destron organization. After rescuing a would-be victim and sheltering her in his home, his family is killed in order to eliminate witnesses, but Kazami himself is spared when Kamen Rider 1 and 2 appear and rescue him.
With his whole family taken from him, Kazami swears vengeance against Destron and asks the Riders to alter him into a cyborg, to which they refuse. When the Riders are captured while in Destron's headquarters, Kazami sets off to save them, but is fatally wounded in the ensuing battle. Left with no choice, the Riders alter Kazami into a cyborg, christening him Kamen Rider V3.