Elfen Lied is a Japanese manga series written and illustrated by Lynn Okamoto. A thirteen-episode anime television series adaptation was produced by the studio ARMS and broadcast on TV Tokyo from July to October 2004. The anime was later licensed in North America on DVD by ADV Films. The anime began airing before the manga was complete; as a result, the plot differed between the two, especially the ending. The title is German for "Elf Song" and takes its name from the poem "Elfenlied".
Elfen Lied revolves around the interactions, views, emotions, and differences between human beings and the Diclonii, a mutant species similar to humans in build but distinguishable by two horns on their heads and "vectors," transparent telekinetically controlled arms that have the power to manipulate and cut objects within their reach. The series is centered on the teenage Diclonius girl "Lucy" who was rejected by human beings and subsequently wants revenge.

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.

• Lucy is a Diclonius girl around eighteen. Lucy has developed strong emotions of hatred and vengeance towards human beings mainly because of how she was treated by the majority of them as a child; they made fun of her horns and gave her insulting nicknames such as "Freak." As a child, she bonded with a dog which was killed right in front of her by classmates, which triggered her first killing. Despite her hatred for most humans, she is in love with Kohta ever since meeting him when they were children, and will not kill him or anyone closely involved with him, most likely out of guilt for the incident that took place years ago. She seems to lack empathy, kills without much concern, and acts somewhat sadistically, often torturing victims before killing (such as Bandou and Nana, although she did not actually kill them); however, towards the end of the series, she begins to show remorse for her actions, especially towards Kohta, whose father and sister she killed. She is aware of her "Nyu" state as revealed in the manga by her worries just before she reverts. Lucy is not her real name; it is revealed in the manga that it is Kaede.
• Nyu is Lucy's split personality that developed after a .50 BMG round ricocheted off the metallic helmet encasing her head.[6] Nyu has a childlike personality and infantile knowledge of the world, forgetting even that she is a Diclonius and how to use or manifest her vectors, leaving her the equivalent to a human being with horns. She initially lacks language skills; however, she eventually learns a handful of words and phrases until (in the manga) she can finally speak properly despite the fact she still uses the nonsensical phrase nyu as her catchphrase. Nyu is innocent and incapable of violent acts, a foil to the normally cold and sadistic Lucy; she is the manifestation of her "good side." Whenever Nyu hits her head or is confronted with violence, she reverts to her sadistic side, Lucy, although is unaware of her actions while in her "Lucy" state. Voiced by: Sanae Kobayashi (Japanese), Kira Vincent-Davis (English)
• Kohta is around nineteen and enters the story when his cousin's family allows him to move in to their closed-down restaurant in exchange for maintaining it while he goes to a local university. Kohta has repressed traumatic memories of his father's and sister's deaths during his childhood. Because of his repressing his memories, Kohta does not remember Lucy from when he met her earlier as a child, nor does he remember the child Yuka (which causes problems for him and Yuka due to Yuka's feelings for him; she is hurt at being forgotten). Due in part to his loss, he has a soft spot for girls in trouble and is extremely generous and protective of the girls around him. He constantly has flashbacks, like many other characters, that do not make any sense to us. He is more forgiving in the anime, but when he gets his memories back in the manga, he is unforgiving towards Lucy for killing his father and sister. Even so, he also remembers the happy memories that he shared with Lucy and loves her despite the horrible things she's done. Voiced by: Chihiro Suzuki (Japanese), Adam Conlon (English)
• Yuka is Kohta's cousin. She is around nineteen and last saw Kohta when they were ten, during the summer when Kohta's family visited (just before Kohta's father and sister were murdered). When Kohta moves to Kamakura to attend the same university as her, she moves in with him at the Kaeda House Inn. She has had a crush on Kohta since childhood, and secretly hopes that they will finally be together. She is uncomfortable with Nyu's attachment to him, and often feels anger at Kohta for not understanding her feelings toward him. Voiced by: Mamiko Noto (Japanese), Nancy Novotny (English)