Doctors Kazamatsuri and Onizuka are geneticists researching cures on diseases such as AIDS and cancer by performing experiments to strengthen the human body. The test subject is Shin Kazamatsuri, motorcycle racer son of Doctor Kazamatsuri. Unknown to them, their operation is funded by a syndicate group, who plan to use this research to have the bodies of men strengthened for their own gain—they have already been experimenting in the field of cyborg soldiers, to a less-than-successful attempt. However, they did not count on Onizuka's own secret ambitions; the mad Onizuka wanted to create a new species, by fusing a grasshopper's DNA with the test subject's, in order to start a new civilization and be their god. He has tested on himself, but seems to be having greater success with Shin.

Shin Kamen Rider: Prologue

When Earth is tearing itself apart by means of crime, pollution and war, aliens choose the time to invade, taking advantage of the lowering of everyone's guard. The Japanese government establishes an elite police organization known as Blue SWAT to combat the aliens, known as the Space Mafia. The aliens attack by possessing humans to obtain their goals. When an alien possesses the chief of the Blue SWAT unit to infiltrate the organization, it manages to completely demolish their building of operations and murder all but three SWAT members; Shou, Sara and Sig.