Ryo Tanaka

100 years ago, titans suddenly appeared on Earth. Soon, human civilization veered on collapse due to the titans. Humans then built a giant wall to defend themselves. Within the giant walls, humans lived in peace, but, 100 years later, the giant wall is broken.

High school student Shun Takahata is bored. Bored with the day-to-day monotony of school and life, he prays for change, for something exciting. Suddenly, he and his classmates are forced to play deadly children's games and facing terrifying creatures from a talking Daruma doll to a sharp-clawed lucky cat.

A detective investigates a series of murders. A possible serial killer might be on a rampage, since the crimes are in the same vicinity, by the same method. However, as evidence points towards the detective, a ghost in red follows him, and he begins questioning his identity. His realization of what seems to be reality results in something far larger and more sinister.

Dormant, experimental cells begin to awaken inside their human hosts, turning them into creatures called 'Amazons'. Two Amazons- Jin Takayama and Haruka Mizusawa- transform into Kamen Riders Amazon Alpha and Amazon Omega, aiming to exterminate the growing threat.