Pure Evils who are enigmatic. They are shrouded in mystery when they first appear with many important aspects of their character not being known. Maybe they might not always appear physically, it could be in a tome or something sacred that was left about these characters or could be imprisoned or currently dead and waiting for someone to resurrect them. However, since these Pure Evils are being mysterious at first, when they are revealed to be the main villain of these stories, the overarching Villains, or even just another antagonist, not only does it cause their reveal of their crimes to be much more horrifying, but it also reveals they were much worse than how the audience thought of them at first.

Example: Muzan Kibutsuji: Before Tanjiro left to become a Demon Slayer, he was told by Sakonji Urokodaki that the person he should look for was Muzan, as he is the first demon and predicted that he would have knowledge on how to turn Nezuko back into a human. However, as Tanjiro meets Muzan posing as a human with a family and later saw him turn a random person in the Tokyo Festival into a demon who attacked an innocent civilian, this confirms he is the reason behind the Kamado family's slaughter, including worser crimes done in series and past, darkening the tone of the story more than it already has.

Even after their defeat, it also leaves the audience with little, many, or uncountable number of unanswered questions.