Shiro Kazami accidentally witnesses a murder by the evil organization Destron, making him their next target. Destron retaliates, which involves Kamen Rider 1 and Kamen Rider 2. Taking the fight to Destron, the Riders infiltrate their base, but Shiro is gravely injured in the process. Left with no choice, they turn Shiro into a cyborg. Now, Shiro uses his new power as Kamen Rider V3 to protect humankind against Destron.