Karen was the priest in the party which set out to kill the Monster Lord Alice XV. Along with Marcellus, Lazarus, and Merlin, she realized too late of Alice XV's wishes of coexistence and prepared to spread her dreams.
However, a young Alice XVI appeared and killed Karen and Merlin out of blind rage. Killing the woman they both loved, Marcellus and Lazarus founded Ilias Kreuz out of vengeance.