Elfen Lied

Elfen Lied takes place in Kamakura, Japan, focusing on a new strain of the human race, Diclonius, similar to human beings but different at the genetic level and notable due to physical abnormalities, particularly a pair of short horn-like protrusions. One such Diclonius, Lucy, is the main character of the series: Initially held in a facility built for experimentation, located off the coast of Kamakura, Kanagawa Prefecture, she manages to escape and wreak havoc, but is injured in the process, an event which causes her to develop a secondary, child-like personality known as Nyu.
Lucy is found by two locals, Kohta, who studies at the local university, and his cousin Yuka. They take her in, and become involved with the numerous, often brutal, attempts to recapture her by a Special Assault Team and a number of other Diclonius, who shift from oblivious to murderous frequently. Other characters include Bando, an SAT trooper mauled by Lucy and infected with a virus, and Kurama, a carrier of the virus.
YouTube Preview Image