One night, Shirou Kazami accidentally witnesses a murder by the evil organization Destron, making him their next target. In their first attempt, they planted a bomb pebble into his coffee, but the attempt was foiled when Shirou's sister, Yukiko, surprised him, causing him to spill his coffee. In their second attempt, they attacked him while practicing motorcycle racing with Tobei Tachibana. In their third atttempt, a Destron soldier, disguised as a doctor, tried to put a poison shot in Shirou, while he was being transported to the hospital (after Destron's second attempt), but Shirou regains consciousness and kills the soldier. Meanwhile, a young woman named Junko Tama stumbled upon Destron's base. Suddenly, she was attacked by Destron. While trying to escape, she ran into Shirou, who was heading home on his motorcycle, but Shirou didn't see the Destron soldiers. Surprised, Junko fainted and Shirou took her home. While Junko was being taken care of by Shirou's family, Shiro reported her story to the police. When he returned home, he found his family being murdered by the Hasami Jaguar, a jaguar monster with blades for hands. Hasami Jaguar then prepares to kill Junko and Shirou, but is stopped by Shirou's high school teacher, Takeshi Hongo, who transformed into Kamen Rider 1. Shortly after he drove off the Destron forces, Kamen Rider 2 shows up, but too late. A vengeance-fueled Shiro asked the Riders to turn him into a cyborg, but the Riders refused, explaining to Shirou what would happen if he did get turned into a cyborg: he wouldn't be able to live up to his family. Then the Riders asked Junko for the location of the Destron base she stumbled upon earlier. The next day, the Riders infiltrate the base, only to get caught in a trap. Shirou shows up and saves their lives, but gets injured in the process. The Riders had no choice but to turn Shirou into a cyborg. When the Riders were attacked, and almost killed, by Kame Bazooka, Shirou shows up as Kamen Rider V3. Now, Shirou uses his new power to protect mankind against Destron.