The Coppelion is a name given to a race of humans with natural antibody towards radiation through genetic manipulation, tasked to undergo missions deep within the now-irradiated Tokyo City.
They were named after Coppélia, the doll that became the central point of the ballet play of the same name, and ion. Aoi stated that the name was given to represent the fact that they were living dolls created through genetic engineering, just like their namesake doll.
Physically, the Coppelions, cloned from other individuals, are the same as normal humans, albeit they were genetically modified to possess a natural antibody known as "ion exchangers" that, as Ibara puts it, works like plants' photosynthesis process, at which the radioactive ions are absorbed by their skin and released as harmless ions, like how plants absorbed carbon dioxide and releases oxygen, thus ionizing radiation possesses no danger for them regardless of concentration and intensity, allowing them to survive even on places with extreme levels of radiation such as the Daiba Nuclear Power Plant’s sarcophagus that would otherwise kill a normal human even with HAZMAT suits. However, this ability does make their skin appear to be much paler in comparison to normal humans.
Other than immunity towards radioactive hazards, the genetic modifications they have also allows the Coppelions to regenerate their wounds much faster than a normal human would, especially when on an environment rich with oxygen, although the rate of their regeneration still depends on each individual. It also bestowed them with various unique abilities, such as enhanced physical strength (Ibara and Shion), enhanced senses (Taeko), elemental manipulation (Kanon and the Mizoguchi brothers), improved regeneration ability (Haruto), interaction with the dark matter (Aoi and Mana), particle manipulation (Meisa) and spatial manipulation (Setsuna).
However, the Coppelions are far from perfect, for they still have many flaws. They might experience "sudden deaths" (突然死) after their DNA, which is repeatedly replicated, deteriorates to the point they can't be recreated anymore, which is seen happening on a female member of the Exploration Unit. Their unique type of blood also prevents them from receiving blood transfusion from normal humans; they must receive blood transfusion from other Coppelions in the same year. Their gamete cells are still vulnerable to radioactivity, making them unable to reproduce; for this reason, their reproductive organs are removed from their body for donation. In addition, the second-year Coppelions also suffer from a dangerous defect in which their body constantly releases free neutrons, making them hazardous to any living beings around them except the other Coppelions.
Later on, Haruto Kurosawa, with indirect assistance from Dr. Coppelius, managed to find the formulation to correct the Coppelions' defects; because they are DNA-related, reverting them back to their default state through a special method known as "initializer" will fix the defects, but this means that the Coppelions will have to lose their genetic modifications, including their antibody from radiation and unique abilities, in the process, essentially turning them into normal humans.
The Coppelions passed the traits of the one they were cloned from, especially their personalities and judgement abilities. The most noticeable is Haruto and the Ozu sisters; the former, because he was cloned from the Coppelions' own creator Dr. Coppelius, was just as genius as his progenitor are, and the latter, because Kuon Ozu, the famous actress they are cloned from, is a sadistic serial killer, was just as murderous and psychopathic as their progenitor are.
All Coppelions served for their namesake unit within the Japanese Ground Self-Defense Forces’ Third Division. They all studied in their own Technical School located in Osaka accessible through a monorail system, and lived in their own house.
The Coppelions are always seen wearing their school’s uniforms in their mission.
The Coppelions are created by Dr. Matasaburo Itami sometime after the catastrophic meltdown of the Daiba NPP, with the third-years are born in 2018, two years after the event. Previously, he, under the alias of Dr. Coppelius, was engaged in embryonic stem cell research and genome analysis, but because such field was always become subject of moral and ethical concerns, he was eventually forced out of the scientific community and are on the verge of bankruptcy until the Daiba NPP meltdown happened in 2016, which became the chance for him to realize his dreamed project with funding from the government.
Dr. Coppelius' work was halted when he was expelled from his own laboratories in the Expo Park through the scheme planned by the Three Professors, who continued his work with their own ways that turned out to be unethical, through human experimentations.
- The Coppelions' radiation antibody through ion exchanges remains fictional because while such mechanism do exists in real life, so far it is still unable to exchange radioactive ions just as the Coppelions' antibodies do.
- There are no known organism with complete immunity against radiation as the Coppelions; the most radiation-resistant organism, the bacteria Thermococcus gammatolerans, are capable of withstanding an acute dose of about 30,000 Gy.
- The reason why the Coppelions are not wearing military uniforms is explained in the Site Story, which are three special manga chapters first published in the Weekly Young Magazine in Fall 2013 and bundled with the first, third and fifth volumes of the BD/DVD.