Alter

"Every creature has the potential for villainy and evil, the problem is the subjectivity of it. And yet more often than not darkness will be accompanied with evil. How insensitive."

- Azazel explaining Alter Alternative (代替, Daigae), otherwise known more commonly as Alter (アルター, Arutaa), is a Magic Phenomenon that revolves around the "materialization of one's inner evils", essentially bringing out the worst in an individual in a process known as "Darkening" (黒化, Kokuka).

Trivia

 * The name "Alter" is inspired by the similar concept of the same name from the Nasuverse, with the most famous example being "Saber Alter".