While cults aren't particularly common in anime, their inclusion makes for some seriously twisted storylines. They can produce some of the creepiest villains imaginable, even though some of them turn good when the brainwashing wears off. They can also provide some truly sympathetic backstories for all kinds of characters.
While some use the word to refer to any new religion, a cult needs to have a few specific features in order to qualify. According to psychiatrist Robert Jay Lifton, a true cult requires a charismatic leader, an initiation ritual that brainwashes inductees, and coercive motives. Anime cults manage to achieve all of these prerequisites, and because they exist in a fantastical, animated world, their sick goals often put the most terrifying real-life cult stories to shame.