Elfen Lied is a very psychological anime and contains a lot of graphic violence (blood and gore). There is near nudity throughout the series, therefore, it's for mature audiences only.
This anime has so much meaning behind the story. It deals with a mutant species called Diclonius, which look like humans, but have two horns on their head called "vectors." These vectors are telekinetic arms that extend out certain distances, which is different for each Diclonius, and can cut, grab, crush, and kill whatever it wants. The main character is a girl named Lucy who, as a child, was shunned by humans because of her horns. Because of the torment, she is seeking revenge against all humans.
Lucy escapes from a experimental facility, Kanagawa Prefecture, and is injured causing her personalities to split. Nyu, the child-like form of Lucy, is her counter personality. Kohta and Yuka, cousins, find the girl on a beach and take her home. A Special Assault Team is sent out to retrieve her as well as other Diclonius. Kohta developes a close relationship with Lucy/Nyu, but there's a dark secret. He has forgotten his memories from his childhood; he no longer remembers anything about how his family was killed. However, Lucy does know.
Elfen Lied deals with a lot of topics such as prejudice, alienation, forgiveness, humility, and so much more. It causes you to really think about whose side your on. At times, you'll hate the Diclonius for what they do, but other times, you understand their hardships and have pity for them. Every character changes from how they were at the beginning. I can't think of one character who doesn't grow in some way.
Even though, it's only a 13 episode anime, it ends very well and doesn't leave any bad loose ends. Other reviews say that the ending is too abrupt and is full of loose ends. I disagree. If you follow the series well enough and put some things together on your own, which is the purpose of the psychological genre, then the ending makes sense. The loose ends, for me, were good ones that keeps you thinking about what happened. They aren't ones that will cause you to be angry.
The music is exquisite. The opening song, Lilium by Noma Kumiko, and the ending song, Be Your Girl by Chieko Kawabe, really fit with the anime and the theme. There is a coresponding manga, however, the anime series was created before the manga was finished causing mass differences between the two. The manga is 12 volumes. This is an anime that both I, a female who loves supernatural romance and more realistic anime, and my husband, a male who enjoys more of the action and adventure anime, loved. I'd recommend it to anyone...as long as you can withstand the gore.