Parasite Dolls or Combat servitor bodies are the humanoid robots which houses a Parasite inside. They were created by Ninth Research Institute, under the impression Retsu, got from Pixie which has a parasite inside of its own.
Background:
Using one "original" parasite, which they got at end of Visitor Arc, Kudou successfully find a method to "multiple" (or divide) them. Later they confined those new parasites, inside humanoid machines, which are envisioned to be a live combat weapons/ soldiers, thus creating a Parasite Dolls or P-dolls.
In order to keep them under control, Loyalty Programming magic was applied.
After their "failure experimentation" during Steeplechase competition, further production of these dolls were stopped and already created ones (sixteen, in count) were sealed.
During Invasion Chapter, Minoru released those seals and starts "commanding" them.
Appearance:
These Combat servitors crafted for military use specialized in processing intelligence during combat. At first glance, the slender body boasted little in way of power. Yet, this body garbed in female combat fatigues contained both might and agility that belied its outer appearance.
There was no helmet or cap because the short strands of hair were sensory devices for air and water currents. There were no goggles or protective visors because the eyes were designed to protect the light sensory devices within. The skin was composed of bulletproof composite material, the joints were rotors capable of swift motion, all coupled with a cooler beauty than even Pixie. This feminine robots was Female combat servitors.
Combat ability:
These dolls did not use “Magic”, but relied on “ESP”. The combat prowess of these P-dolls was in no way inferior to first class Magicians, and the activation speed of their superpowers was superior to modern magic as well.
From detecting the other’s silhouette to beginning to move, it's speed was beyond human capability. It was not only the superb information processing speed of an electronic brain, but a machine built specifically for combat.
Each doll has different ability and at that time, four dolls were designed to fight as one -mutual cooperation- these four were called as the "Prime Four". The Prime Four was strong enough to go toe on toe with Ooguro Ryuuya of 101 Independent Magic-Equipped Battalion. In other words, they are successfully made as active front-line combat weapons.
Among the Sixteen Parasites Dolls known "ESP" abilities are Telekinesis, Pressure Slash, Self-acceleration, Repulsion barrier, Gravity control magic, enhanced "sound" ability, to a point of easily casting Phonon Maser.