Showa Kamen Rider Jump (Part 1)

From the introduction: The year is 1971. Disco is just starting to become popular, the Cold War is still going strong, and the Vietnam War is about to end. However, things are not what they seem. A mysterious evil organization known as Shocker is aiming to take over the world. To further its agenda, Shocker recruits its agents through kidnapping, turning their victims into mutated cyborgs and brainwashing them. However, one victim named Takeshi Hongo escaped just before the brainwashing process could be enacted.