The Diclonius, a mutated homo sapien that is said to be selected by God and will eventually become the destruction of mankind, possesses two horns in their heads, and has a "sixth sense" which gives it telekinetic abilities. Due to this dangerous power, they have been captured and isolated in laboratories by the government. Lucy, a young and psychotic Diclonius, manages to break free of her confines and brutally murder most of the guards in the laboratory, only to get shot in the head as she makes her escape. She survives and manages to drift along to a beach, where two teenagers named Kouta and Yuka discovers her. Having lost her memories, she was named after the only thing that she can now say, "Nyuu," and the two allow her to stay at Kouta's home. However, it appears that the evil "Lucy" is not dead just yet...
(taken and edited from ANN)

Picture	Real Name	Description
	Lucy	A teenage diclonius girl around 18 years old, Lucy has four vectors with a limited range of two meters.[4] However, she can be swift and lethal within that range, and will use any nearby objects as high velocity projectiles to kill at greater distances. She is also capable of stopping or deflecting most standard ammunition when she concentrates on the task. Lucy hates humans mainly because of how she was treated by her human peers as a child. Consequently, she discounts non-diclonii, claiming they are not real people. She seems to lack empathy, kills without much concern, and acts somewhat sadistically. Despite this lack of concern for human life she will not harm Kohta.
	Nyu	a split personality of Lucy that developed after a .50 BMG round ricocheted off a metallic helmet encasing her head. 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 a human with horns.
	Kohta	around 19 years old and enters the story when his cousin's family allows him to move in to their closed down inn in exchange for maintenance while he goes to a local university. Kohta has repressed traumatic memories of his father's and sister's deaths during his childhood at Lucy's hands. Due in part to his loss, he has a soft spot for girls in trouble and is extremely generous and protective to the girls around him.
	Yuka	Yuka is Kohta's cousin and is also around 19 years old and planning to attend the same university as Kohta. She moves in with him at the inn after having not seen him in many years. Having had a crush on Kohta since childhood, she is in love with him, and is therefore jealous of Kohta's attention to Nyu, to the point of being very irrational.