Diclonius are a species from Elfen Lied and are believed to be the next step in evolution for humanity. The most powerful of them and their "Ruler" is the Queen of Diclonius Kaede.
The Diclonius are a newly evolved species, arising from and very similar to average Humans, but possessing psychokinetic abilities far beyond any human. For reasons that may be cultural as well as biological, they are often at odds with Humans to the point of threatening to replace them as Earth's dominant sentient species.
While Lucy was indeed the first and 'Queen' Diclonius, in fact, her late mother was the source of the mutation that birthed the virus in her children. Lucy's birth fulfilled the messianic expectations of the well-heeled and highly positioned Kakuzawa clan, a number of whose family members possessed a genetic mutation that gave them vestigial horns. Despite this, their cult-like beliefs, and the literally world-shaking steps taken on behalf of Diclonius supremacy by Chief Kakuzawa, the two groups were unrelated. Sadly, the treatment of the Kakuzawas in feudal Japan and their reaction to it would foreshadow the relations of Humans with the true Diclonii, centuries later. Chief Kakuzawa also believed that the Diclonius were the Oni (Demons within Japanese Mythology) that were meant to surpass and replace Humans when their messiah was born.
Anatomy and Physiology
The differences are both outwardly visible and internal. Their heads have bony protrusions that resemble cat ears, but are in fact a mix of bone and cartilage, possibly the result of an extremely enlarged pineal gland in their frontal lobes. These vectors have the ability to manipulate objects and are precise enough to have cutting power, and can be very destructive when unleashed. They are perhaps telekinetic in nature, and can seemingly break bonds at the molecular level.
Diclonii have the ability to detect one another, such as when Kurama released Nana from the offshore laboratory to search for and retrieve Lucy. Even this ability had limits, as she could not sense her target when she was in her childlike Nyu persona, nor could she sense the Mariko clones (Alicia, Barbara, Cynthia, and Diana) when they were under the control restraints set up by Nousou and the Agent riding herd on them during their assault on Maple House.
Diclonius all heal very quickly and do not scar easily. Diclonius are extremely intelligent, however they are just as emotional as Humans, often more so. Once pushed to the brink, some hear a voice that claims to be the directing voice of their own DNA, urging them to kill as many Humans as possible.
Diclonii all have similar hair colour and eye colour in the anime (shades of purple and pink), but in the manga they have different coloured hair and eyes. The reason for the same coloured hair and eyes in the anime was to tell Diclonius apart from regular Humans, since the anime was so short that it needed to be easily defined from the very beginning.
In the manga, it is mentioned that Diclonii might fall into a coma if they lose one of their hor
ns, and would never return from their lethargic state if they lose both horns. Lucy's horns grow back though and manage to recover from this twice, at least once becoming more like devil's horns than cat ears. Their vectors usually have a limited range of a few meters. Lucy's are able to extend to two meters, and while Nana, Mariko, and her clones are shown to have either more vectors or greater normal range, her raw power is such that it came to threaten the world. However, the use of such levels of power, ultimately turned to healing Kouta's mortal wounds, lowered and then finally destroyed her own body's integrity.
There are two main classes of Diclonii. One is Lucy, the Queen, the others being Silpelits. The Silpelit Diclonius variety cannot reproduce, but instead use their vectors to infect humans, turning their children into Silpelits when they are born. Other types include the many clones of Mariko, who was arguably the most powerful Diclonius and aboy born of Chief Kakuzawa's rape of Lucy's mother, the true source of Diclonius DNA and the vector-born virus, despite being fully human. The Kakuzawa family had, for many generations, believed that they were Diclonii as well, and built up a world-shaking scheme based on promoting Diclonius supremacy, including detonating a missile laden with the virus in the skies over Japan. Though this belief turned out to be mistaken, the threat from the Diclonii kept on even after the deaths of Lucy and Chief Kakuzawa, with the cycle of attacks and retribution ensuring no possibility of co-existence between the races. It is revealed in the final chapter that a temporary world-wide birth ban coupled with the use of the Anti-Diclonius Birth Vaccine helped lead to the end of this threat, though not before the death of at least a notable portion of the world's population. The war's duration seemed to be less than five years, since ten years after Lucy's death, Kouta is seen in the company of his roughly eight-year-olddaughter, meaning at least the birth ban was definitely lifted, indicating near if not total elimination of the threat.
Destructive Instincts 
It is said by some in-story that the Diclonii were chosen by God as the new humanity, born with the instinct to destroy the human race and repopulate the world. In the final episode of the anime, Lucy tells Kouta that "I was born to kill humans". She seems at times to have yet another separate personality born entirely of the DNA-driven Diclonius instinct to kill humans, which may or may not have been responsible for her killing his family, a thought rejected by Kouta himself as an excuse. However, Nana's character, as well as the incidents surrounding Lucy’s past and relations with Kouta, suggests that it is possible for Diclonii to have empathy towards humans, and that their sadistic characteristics develop as a result of their interactions with the world. Barbara, a clone of Marikoclaimed to have also heard this voice. But her personality was shaped by birth and life in a lab, and seemed to have all of Mariko's sadistic tendencies without any of her tempering characteristics. Nana once seemed to have heard it, but was in shock from leaving Kurama and was taunted by Bando as to her lack of a place in the world.
It is entirely possible that the Diclonius species was actually very normal and/or peaceful, and that the voice of hatred they have is only caused by the prejudice being put against them.
Diclonii tend to be heavily discriminated against (infants are often euthanized on the spot) by other humans, and the series makes it unclear whether the often murderous hostility Diclonii show as well is innate or the result of thehatred and contempt shown against them.
Researchers at both the Kakuzawa facility and the government-controlled facility believed the Diclonii to be a serious threat to the human race. Diclonii are for the most part kept in isolation and fed by tubes. When Kurama's daughter, Mariko, is born as a Diclonius, he remembered an incident in which an escaped Silpelit touched him with her vectors. At this point, he realized that this explained his daughter's condition and an explosion of such births, with Diclonii passing on their DNA and causing human parents to have horned children, in theory up to the point that normal humans would be displaced as the planet's dominant species. Lucy mentions the danger to the human race to Kouta in the final episode: "Given just five years, I can ensure that there are more babies of our kind born in the world than there are normal humans."
|“||He is the ultimate Diclonius... I am the father of Adam.||”|
Kaede's Half-Brother was a MaleDiclonii which are almost unheard of and are extremely rare. The only one seen or spoken of in the Elfen Lied series were born through the rape of Lucy/Kaede's long-lost mother by Chief Kakuzawa. Kakuzawa planned to mate both him and Kaede to start a new Diclonius race with himself as the progenitor--or 'God of the New Race' as he clearly said so himself. Like the viable clones of Mariko clones, the boy had a mind-control device implanted inside his head, which kept him under control and inhibited his ability to speak. Towards the end of the series, Lucy was taken back to Kakuzawa's Island HQ and held in a secret underground grotto, where she was told of his plans and introduced to her half-brother, who seemed to recognize their familial connection. Rejecting Kakuzawa's megalomaniacal agenda, Lucy decapitated both him and her half-brother. She then apologized to his headless corpse by saying that neither of them had a right to exist, that their bloodline must end, and that she would also die very soon. This boy was also the half-brother of Professorand Anna Kakuzawa. Despite the Kakuzawa family's racial beliefs, this boy was the only member of their family who had ever been a true Diclonius.
Vectors are the Diclonius' invisible *arms*, likely telekinetic in nature and origin. Vectors can become visible if their vibration frequency is high enough. The number of vectors varies between Diclonii (the most being fifty on #35), and they can be between three and eleven meters long. As she was dying, Lucy unleashed vectors so powerful, they threatened to destroy the world. The Clone Diclonii, created from the DNA of Mariko, had power that, once united and focused, destroyed and sank the island containing the Diclonius Research Institute. Also, because of their unstable genetics, their vectors varied widely in length and power.
Vectors are called arms, but they are in fact powerful energy weapons that the Diclonii likely visualize as arms. They can destroy or repel all but the densest materials, notable exceptions being the specialized prison doors at the Diclonius Research Institute and sniper rifleshells like the .50BMG. Needless to say, any living being targeted by these will not last long. Working as bludgeon to scalpel or anything in between, vectors can bring down a military helicopter, or disturb blood vessels on a target so as to cause death by what is seen as a heart attack or stroke. Vectors are also used in the series to infect human males with the Diclonius virus, causing their offspring to have horns and abilities. Certain Humans may be able to see vectors despite their wavelength, and some have learned tododge them with experience.
Despite being referred to as weapons, vectors have been shown to have non-destructive uses. Mariko, for example, used to them shield her father and Nana from a missile strike. Two of her viable clones, Alicia and Barbara used their vectors to save Nousou from a falling helicopter. They can also be used for any purpose that non-telekinetic arms could be used for. Both individual Diclonius as well as the Vector Attack Craft have used them for transportation. In the last act of her life, Lucy used them to heal the badly wounded and dying Kouta.
In the anime, vectors can be stained with blood, and by this, reveal themselves.
Weakness and Limits
Despite their power, vectors can be disabled. Just as a Diclonius can do a precision strike on a target's artery or vein, so can they disable another's vectors. This would not permanently disable the vectors but would give someone enough time to strike back or escape. Diclonius can see (or sense) their own vectors as well as those of other Diclonius. Extreme pain such as Nana or Mariko suffered when they lost limbs causes a critical lack of focus. Use of the vectors to disable nerve endings can bring about much the same result. Vectors can also be disabled if maintained too long at a high frequency, similar to how muscles not properly limbered can seize up from unreleased tension. Rapid repeated efforts will lead to exhaustion of the vectors and a temporary crippling of their use. The anime shows Mariko suffering from this in the last two episodes. Another limitation is the condition of the Diclonius's horns. If one or both are shattered, not only are the vectors shut down, but the Diclonius can become comatose or even die. Additionally, despite their speed, it is possible to evade and dodge vectors, as shown by Bando against Lucy.
The non-Kakuzawa Diclonius project run directly by the Japanese government, Saseba, sought to exploit the potential of vector-based weaponry, but this proved to be mainly useful in combating Diclonius, not as any sort of viable conventional weaponry.
The vectors abilities depend on their frequency:
- Low frequency = Can go through objects without causing physical interference.
- Medium frequency = Can lift objects and throw them, as well as disrupt blood vessels.
- High frequency = Can slash through wood, flesh, bone and rock. Can carry liquid on surface.
- Extremely high frequency = Highly visible and gain potentially explosive power.
- A Diclonius can see (or sense) their own vectors as well as those of other Diclonius. Most Humans cannot see them. Kouta's little sister Kanae claimed to have seen Kaede's vectors at the Summer Festival, but it remains unknown whether this was the result of an agitated Kaede or because of blood sticking on vectors.