Choudenshi Bioman

Centuries ago, the android Peebo and the Bio Robo arrived on Earth from the destroyed Bio Star. Before entering dormancy, Bio Robo showered five courageous humans with Bio Particles, ensuring that this power would be passed down through their descendants.

In the present day, Dr. Hideo Kageyama transforms himself into the mechanical dictator Doctor Man and establishes the Shin Teikoku Gear, also known as the New Empire Gear. From the Antarctic fortress Neograd, he begins a campaign to conquer Earth using Mecha Clones, Beastnoids, and giant Mechagigans.

Peebo awakens and locates the descendants of the original five humans touched by Bio Particles. With the Techno Braces, they transform into the Choudenshi Bioman and begin their battle against Gear's mechanical empire.

The conflict takes a tragic turn when Doctor Man deploys the Bio Killer Gun, leading to the death of the original Yellow Four, Mika Koizumi. Jun Yabuki is later recruited as the second Yellow Four, allowing the team to continue the fight.

Unlike many Sentai enemies, Gear relies on five recurring Beastnoids instead of a new monster every week. When the Biomen defeat one of these recurring commanders, Gear escalates the fight by launching a giant Mechagigan against Bio Robo.

As the war continues, Doctor Man's own creations begin to reveal the limits of his mechanical worldview. His supercomputer Brain and the android Prince show signs of human emotion, while Prince is revealed to be modeled after Doctor Man's real son, Shuichi. The Big Three learn that their ruler was once human and attempt to rebel, only to be defeated, brainwashed, and upgraded.

The Biomen also face Bio Hunter Silva, a rogue anti-Bio warrior from space, and eventually ally with Professor Shibata, a mysterious scientist developing a conscience circuit. Shibata is revealed to be Shinichiro Gou, Red One's father and Doctor Man's former colleague.

In the final battle, the Biomen defeat Silva and his robot Balzion before entering Neograd itself, bringing the war against the New Empire Gear to its decisive end.

• Choudenshi Bioman The Movie (1984)