Karin is a supposed evil witch version of Kyrie that was introduced in Umineko: The Story of Kyrie. She is a smug and sneering person, who does not miss the opportunity to mock people. She was created by Blushii as a joke, because he wanted to see an outgoing version of Kyrie.
Karin's personality is a bit like Kyrie, but with an added aspect of coldness and evilness. As stated before, she loves mocking people at their expense and harming people. Her favorite hobby is to see how many people she can kill. Karin was created to mock the overly "evil" types of characters, but she herself is not aware of this fact, only Blushii is.
Karin is first created by Blushii after he decided he wanted to see an evil and outgoing version of Kyrie.