Diclonius is the word for the fictional mutant, human-evolved species introduced in the Japanese anime and manga Elfen Lied.

Their physical form is similar to humans, with the addition of two horns on the front side of their head (apparently projections of the cranial bones) these horns may also look like cat ears. For some reason, all female dicloniuses have pink/purple hair. In fact male dicloniuses have lesser skin covered horns, are bald and lack any special powers.

Dicloniuses have a telekinetic aptitude that manifests as several vectors of force (shown as translucent arms with hands that extend from their back). These vectors are capable of exerting a very strong force and can be used to propel objects, for blunt hits, and as very thin slicing tools (in fact, dicloniuses kill normal humans with no trouble by tearing them in half or chopping their heads off).

Each diclonius has a given number of vectors at her disposal, with a fixed arrive at or range. For example, Lucy, a major character in Elfen Lied has four vectors, with a utmost reach of two meters — though of course, she can use them to accelerate objects at a very high speed, exactly as normal humans can fling objects outside the range of their bare hands. Lucy is by no means the mainly powerful diclonius (a little diclonius girl, Mariko, had twenty-six 11-metre-long vectors).

Dicloniuses can also use their vectors to shield themselves from bullets and shrapnel. The ability to turn aside and even stop bullets in mid-air is variable and needy on the caliber and velocity of the bullet (with high-caliber/high-velocity bullets being difficult or impossible to turn aside or completely decelerate) and also on the strength and skill of the individual diclonius.

Dicloniuses are portrayed as a cruel race superior to current humanity, with the single purpose of exterminate the non-mutant Homo sapiens. In fact, they show little compassion or empathy for normal humans, with a few exceptions. Their personalities are more often than not homicidal and sadistic, and they will even kill other dicloniuses with little concern. Dicloniuses do at least seem to show compassion for animals. Around their third year of age they become aware of their powers and the drive to destroy normal humans awakes within them, making them tremendously dangerous. Their containment needs special installations and is vehemently very traumatic for them, which of course does not make them any more amenable to claims of compassion.