The evil organization DARK, led by the sinister Professor Gill, seeks world domination. To build his army of monster androids called Destructroids, Gill forces the brilliant robotics expert Dr. Komyoji to work for him as a prisoner. Secretly, Dr. Komyoji creates a special android to fight back against DARK and protect his two children, Mitsuko and Masaru. That android is Jiro, a mechanical man who can transform into the powerful red-and-blue superhero Kikaider.

The series begins as a massive fire breaks out at DARK’s base. Jiro manages to rescue Mitsuko, but Dr. Komyoji is separated from his children and disappears, suffering from amnesia. Jiro destroys the first Destructroid, Gray Rhino King, and then dedicates himself to protecting Mitsuko and Masaru while searching for their lost father. The trio is often assisted by Hanpei Hattori, a bumbling but good-hearted private detective who provides comic relief.

The middle portion of the series follows a mostly episodic formula. DARK unleashes a new Destructroid each episode to carry out a specific scheme, from taking over a dam to terrorizing an amusement park. Jiro, as Kikaider, confronts the monster and typically wins using his finishing move, the Denji Endo (Electro End). A major obstacle for Jiro is his incomplete conscience circuit. Professor Gill uses a hypnotic flute whose sound causes Jiro intense pain and can even prevent him from transforming into Kikaider, forcing Jiro to find creative ways to block out the noise. During this time, the amnesiac Dr. Komyoji appears as a background figure, occasionally and unknowingly repairing Jiro when he is damaged. Several episodes stand out for their emotional weight. One features Gold Wolf, a Destructroid given an incomplete conscience circuit by Dr. Komyoji, whom Jiro is forced to destroy with great remorse. Another episode, Black Spiny Anteater, presents a rare view of Kikaider as a terrifying killer from the Destructroid’s perspective.

The series shifts dramatically in its final story arc. Professor Gill’s flute control over Jiro reaches a peak, causing him to attack Dr. Komyoji. DARK then captures the doctor and frames Jiro for his murder. Damaged and unable to speak, Jiro cannot defend himself and becomes a fugitive, hunted by the police with only Mitsuko believing in his innocence. At this point, a new, more powerful android appears: Hakaider. He is Dr. Komyoji’s ultimate creation, but he is a cyborg, built by force and containing the doctor’s own brain under the control of an evil circuit, making him the dark mirror of Kikaider. Hakaider battles Kikaider but must retreat due to needing periodic blood transfusions from Dr. Komyoji’s body. Hakaider takes the human form of Saburo, presenting himself to Masaru as a new brother android created to stop the now supposedly evil Jiro.

The climax sees Jiro destroyed by the Destructroid Red Mine Toad. Hanpei collects the pieces of his body and delivers them to Mitsuko. Driven mad by the loss of his only purpose for existence, Hakaider turns against DARK and destroys Red Mine Toad. He then locates the partially reassembled Jiro, but refuses to fight a helpless opponent, allowing Mitsuko to finish rebuilding him. In the final three episodes, a rebuilt but still malfunctioning Jiro lures Hakaider away from Dr. Komyoji’s children. Professor Gill sends his last Destructroid, White Bone Flying Squirrel, to destroy Hakaider. After Hakaider loses the battle, Jiro returns his body to Mitsuko, who successfully restores Dr. Komyoji’s brain to his original body. The recovered Dr. Komyoji fixes Jiro’s transformation circuit, and Kikaider destroys the final Destructroid. Professor Gill, rather than be captured, destroys himself and the DARK base. Dr. Komyoji leaves Japan with his children, while Jiro chooses to remain behind to continue his journey of self-improvement.

It should be noted that Tobidasu Jinzō Ningen Kikaidā is the title of a theatrical 3-D film released on March 17, 1973, during the show’s original run. The 33-minute movie features a standalone story in which Professor Gill uses a machine to resurrect all the Destructroids previously destroyed by Kikaider, forcing the hero to battle them again. While the title is often associated with this film, it is also sometimes used to refer to the original 1972 television series.