A Kishin is a super-natural and powerful being, created when a human soul has fed on the souls of a large number of innocent people. Kishin themselves are rare, and as of now there are none in existence. Shibusen aims to prevent the creation of any Kishin, for they hold god-like power. They are not to be confused with Kishin Eggs.
What is a Kishin Egg?
A Kishin Egg is something that is on its way to being a Kishin, but has yet to reach it. People who have murdered and eaten the souls of other humans, and have become addicted to them. These people lose all aspects of humanity, even the ability to think as one. They are rather common, but still dangerous.
What are Witches?
It is important to note that Witches in this world, are not exactly the same as Witches in other worlds. If you are a Witch wherever you came from, you have nothing to fear.
Witches, as defined here in this world are women with great magical power, who are effected by something called the Sway of Magic. This means that their magic is something that they are instinctively driven to use in accordance to its nature. Since most magic is offensive, this turns them into people who seek to kill and destroy. There are very few exceptions, but those who do not bring harm to others, and not hunted down.
All Witches it seem have an animal association.
Arachne - Spider Witch - Deceased.
Considered a traitor to her people, Arachne was the one who created the first Weapon by fusing a human soul, a witch soul, and a weapon. Her motives were unclear, but she aided in the evolution of Kishin Eggs as well.
Eruka - Frog Witch
Assisted in the aid of Kishin Asura's revival, and lackey to Medusa. Still at large, though believed to be responsible for the recent rain of mutant frogs, and Crane's escape.