Madness (発狂, Hakkyō) refers to the spectrum of behaviors characterized by certain abnormal mental or behavioral patterns. In the world of Soul Eater, however, Madness also takes the form of a force, able to influence an individual in a plethora of ways mentally or even physically.
According to Franken Stein, every being in the world of Soul Eater has a bit of Madness within them, however small that it might be, within the souls. Due to the nature of the Madness Wavelength, those who emit a particular type of Madness can sway the Madness within an individual. In addition, Madness itself is contagious and is able to spread itself through even the world. Madness itself, if left unchecked, can take a hold of even the general populace of the entire world, possibly arousing the evil within an individual or boosting its hold over them.
Influences on personality
Madness can manifest from things seemingly inoffensive or senseless. For example, Kid's obsession is due to the Madness of Order influencing in which, when fueled, prompted Kid to think he should erase everything for the perfect sense of order. Another example is Black☆Star's desire for power without any important reason. This is somehow linked to his father, White☆Star, as he took the Path of the Demon. Both cases however show that Madness can manifest from obsessive and otherwise uncontrolled thoughts or beliefs, but can be prevented, if guided or restrained properly.
Main article: Madness Wavelength As stated by Stein, every person has a little madness inside them. But select individuals not only have Madness, but emit a powerful Madness Wavelength capable of influencing individuals to perform certain actions depending on the the type of Madness Wavelength.