Masaru Aso was the lab assistant of geneticist Doctor Mochizuki, used as one of his experiments related the creation of the Neo Organism, enabling him to transform into a grasshopper-like being called Kamen Rider ZO. He fled into the mountainside and went into a coma before he was awakened by a telepathic call two years later with an unconscious urge to protect Hiroshi Mochizuki, the son of Doctor Mochizuki.
The story begins with three Aliens in human form preparing for a ritual to feed the Fog Mother's "siblings". The Fog Mother last came to earth during the Prehistoric Age and is the cause of the extinction of the dinosaurs. Kenji and his kid sister are in the mountains, investigating all the deaths of animals and trees there. The Fog Mother sends the three aliens, "Gorai", "Zuu", and "Agito" to kidnap Kenji's baby sister for the sacrifice.
A bizarre medical exam of a nude woman by several doctors and scientists reveals that their latest subject has committed suicide before giving birth to one of the mutant creatures they had placed within her body. So, an investigative crew of scientists (along with a large human mutant cyclops creature) heads out to the city streets to obtain a new donor/victim in the form of a young girl. Gore and Z-Grade mayhem ensue.
