I have finished Elfen Lied. It is a great manga but I not recommend it to the younger audience. It is quiet gory and unappropriate for them to be reading. I must have a sence to pick mangas that make me want to cry, because when Lucy/Nyuu was dying, I cried. Well here is a pic and summary of the manga.

The Diclonius (two-horned human) are mutants created by humans. It has a special ability that can be described as a sixth sense. These mutants have enough power to exterminate the whole human race. Afraid of their powers, people isolate them in research labs to be studied.

One Diclonius girl, Lucy, breaks out of confinement, kills her guards and escapes. She falls into the ocean after being shot and ends up on a beach. There, she meets Kota and Yuka. They name her Nyu and begin to live with her.