Several years after being subjugated to an inhumane experiment, Masaru Asou wakes up in a forest, hearing the cries of an unknown voice to protect Hiroshi Mochizuki, the son of the scientist who experimented on him. Hiroshi's life is endangered by a humanoid monster, but is saved by Masaru, who becomes the cyborg Kamen Rider ZO. Masaru then realizes that Professor Mochizuki has gone missing for the past two years and the
