A plane crashes deep in the Amazon rainforest, leaving a young Japanese boy named Daisuke Yamamoto as the sole survivor. He is discovered and raised by a hidden Incan tribe, who name him Amazon. Living as a feral child, he grows up in the jungle until the day the Ten-Faced Demon Gorgos and his evil organization Geddon massacre the village in search of a powerful artifact known as the GiGi Armlet. The tribe’s elder, Bago, performs a mystical Incan ceremony on Daisuke, transforming him into the beast-like Kamen Rider Amazon, before giving him the armlet and dying.

The setting shifts to modern Japan, where Amazon arrives to confront Geddon. He is a wild man who barely speaks Japanese and fights with savage, animalistic movements, biting his enemies and tearing at them with his claws. He befriends siblings Masahiko and Ritsuko Okamura, whose professor uncle was an acquaintance of Elder Bago and is killed by Geddon for his knowledge. Also assisting Amazon is Tobei Tachibana, a veteran motorcycle mechanic and ally of previous Kamen Riders who helps the jungle boy adapt to civilization.

The first major narrative arc follows Amazon’s war against Geddon. The organization is led by Gorgos, a grotesque entity with ten faces embedded in a giant boulder-like body who possesses the counterpart GaGa Armlet. Gorgos seeks to combine both armlets to achieve world domination fueled by human blood. Over the course of brutal battles against Geddon’s various Beastmen monsters, Amazon begins to learn Japanese and the true nature of his power. He eventually confronts and destroys Gorgos, but the GaGa Armlet is stolen by a new, more menacing force.

This introduces the second arc against the Garanda Empire, a more technologically advanced terrorist organization that emerges from the shadows to claim the GaGa Armlet and conquer Tokyo. Led by the mysterious Great Emperor Zero, Garanda launches a series of catastrophic attacks on the city, including attempts to flood Tokyo with fire and trigger massive earthquakes. The narrative intensifies when a friendly Beastman, the Mole Beastman named Mogura, defects from Geddon to become Amazon’s tragic ally, eventually sacrificing himself. The story concludes with Amazon infiltrating Garanda’s subterranean base, where he combines the GiGi and GaGa armlets to negate Emperor Zero’s powers. In a final, ferocious battle, Amazon destroys Zero and the Garanda Empire, completing his mission.

In 2016, the story was rebooted with a darker, more mature web series titled Kamen Rider Amazons, set in a separate continuity. This version takes place in a contemporary city where a secret laboratory accident released man-eating creatures also called Amazons. The plot focuses on two contrasting characters: Haruka Mizusawa, a weak-bodied young man who transforms into Kamen Rider Amazon Omega, and Jin Takayama, a grizzled older man who hunts his own kind as Kamen Rider Amazon Alpha. The series explores the moral ambiguity of eradicating creatures that were once human, culminating in a 2018 theatrical film, Kamen Rider Amazons: The Last Judgement, which concludes the reboot's storyline.