Yami

Yami is a female who wants to start a war against the wizards of the world. She is also the main antagonist.

Chimera Rampage arc
Yami was mentioned by Kaminari. Apparently, she's waiting for an eclipse to start a war. Though not seen, she used Dark Magic in order to retrieve and bring him back to the base.

Personality
Considering that she wants to start a war shows that she's a sociopath. What has been shown of her, she did not care for her followers and only wanted them for carrying out her dirty work. An example is when Kaminari return to base, he reported that he vaporized Mari Village. This sparked Yami to attack him and force her other followers to just stand still and watch.

Behind the Scenes

 * Yami means Dark.