Sex Machine tells of the affable but simple Hiroshi, who during one sweltering summer in a small, parochial town, moves in with his girlfriend, Haruka. Their lovemaking is as athletic as it is bizarre but a dark storm comes looming when Haruka's ex boyfriend comes knocking at the door.

A bizarre medical exam of a nude woman by several doctors and scientists reveal 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) head out to the city streets to obtain a new donor/victim in the form of a young girl. Gore and Z-Grade mayhem ensue.