A being effected by the 'Vector Syndrome', a fictional genetic disorder from a horror anime series 'Elfen Lied'.
The effects of the syndrome are horns that come out of the being's skull and invisible,'telikenetic', arms called vectors that come out of their back. 'Lucy', thought of as the 'queen of diclonius', was one of the original children that suffered from this syndrome and was tested on. Her vectors have an average of 2 meters, while the later beings effected by it have a greater length ('Nana's vectors can go up to 3 meters, Moriko's can reach up to eleven meters). The syndrome is spread by the vector's touch to the head.
The diclonius aredangerous creatures that are merely meant to kill all subordinate beings.