Kaede, known as Lucy and Nyu, is the central character of the series. She is a Diclonius, a mutated human subspecies distinguished by two horn-like protrusions on her head and the possession of invisible telekinetic arms called vectors. As the original Diclonius, she is sometimes called the queen of her species. Her backstory is defined by severe childhood trauma. Born to human parents, she was bullied and ostracized for her horns. A pivotal event occurred when a group of classmates killed a puppy she had befriended, beating it to death in front of her. This triggered her first violent outburst, during which she murdered the children involved. She was subsequently captured and held in a government research facility for several years. The personality known as Lucy is the primary, vengeful identity that emerged from this abuse. She harbors a deep hatred for humanity, seeing non-Diclonii as subhuman and often killing without hesitation or remorse. She can be sadistic, maiming or torturing victims before killing them. However, she is not purely evil; she retains the capacity for love and guilt, specifically toward Kouta, a boy from her past who showed her kindness. She killed Kouta's father and younger sister out of jealousy when she saw him with his cousin Yuka, an act she deeply regrets. To avoid hurting him further, she actively suppresses her own violent nature when he is present. After her escape from the facility, a bullet wound to her head created a secondary, dissociative personality called Nyu. Nyu is childlike and innocent, initially unable to speak beyond the sound nyu. She possesses no memory of Lucy's past and has no capacity for violence. She is gentle, affectionate, and dependent on those who care for her, most notably Kouta and Yuka. Over time, she learns to speak more normally, though she retains some of her childish mannerisms. The two personalities are linked by physical triggers: a blow to the head or a moment of extreme danger causes Nyu to revert to Lucy, while kindness, affection, or Lucy's own guilt can push Lucy back into Nyu. Nyu's existence is partly a product of trauma and partly Lucy's subconscious wish to hide from Kouta and atone for her crimes. Throughout the story, Lucy / Nyu serves as the primary protagonist, but her role is ambiguous, as she is both a victim and a perpetrator of extreme violence. Her motivations shift between revenge against humans and a longing for acceptance and love from Kouta. Key relationships drive her development. Her bond with Kouta is the emotional core; she loves him deeply but is haunted by the murder of his family. Her interactions with Yuka are strained by jealousy, though she refrains from killing her. Other Diclonii, such as Nana, become foils, with Lucy showing rare restraint. Over the course of the series, Lucy begins to question her hatred and seeks redemption, often trying to maintain Nyu's presence as a way to protect Kouta from herself. In the manga, a third, purely instinctual personality ultimately emerges, representing the Diclonius drive to exterminate humanity. Lucy / Nyu's notable abilities include her vectors, which are invisible arms that can extend about two meters. Within that range, she can slice objects, lift heavy weights, stop or deflect bullets, and use anything as a high-velocity projectile. She has six vectors, more than most Diclonii. Her horns are sensitive and can sense other Diclonii, and damage to them can cause her to lose consciousness or switch personalities. Nyu, when necessary, also demonstrates the ability to use these vectors, albeit with a less violent intent. Over time, her vectors grow stronger and longer, especially in moments of extreme emotional stress.