A "Frankenstein" is a non-human monster created by a process invented by Dr. Victor Frankenstein roughly 150 years before the main plot of the manga. "Humans that are not human", a Frankenstein is made from human body parts, electrodes, 1.21 gigawatts of electricity, and a temperature of bellow 0 Celsius.
A Frankenstein is far more powerful then a human, needing little rest and possessing a body far more powerful then any human. They do not age, and their only major weakpoints are sutured flesh, which breaks apart easily, and their Electrodes, which they need to live.
Every Frankenstein needs electricity to recharge them, the electrodes are used to pump electricity into their bodys every once in a while. Every Frankenstein has Electrodes somewhere on their body, if these broke then the Frankenstein would die.
Some scientists are able to design specialized Frankensteins with improved functions. A basic example would be Lord Cadavers two headed Frankenstein, while an advanced example would be Dr. Richter's 8 advanced Frankensteins, which are capable of flight or massive destruction.
A Frankenstein can by made of any number of corpses, but its memories and personality tend to be almost random. It may carry memories from its old life, but it's personality may be warped beyond recognition. It may be the same person, but with no memories. In the worst case, it becomes a monster with no memories and no mind.
A motto of both Polar Route and Blitz, as well as doctors and Frankensteins in general, is that anybody who would ever willingly involve themselves in the world of Frankensteins is either evil or insane.
- 1.21 gigawatts is a reference to one of the favourite movies of the author "Back to the Future", in which a lighting bolt generates this amount of power.