Total Human Cyborg Replacement Project

The Total Human Cyborg Replacement Project (人体のサイボーグ全置換プロジェクト) was a cyborg experiment carried out in Academy City.

Principles
The project was an experiment which was meant to test various forms of cyborg technology and its compatibility with the human body over the span of a year, gathering data from the cybernetic treatments to aid in further development. The test subject was cyborg researcher Kuriba Ryouko, who had volunteered in order to gather data for the many different cybernetic parts which would be necessary to save her ill mother, who had only a couple of years left to live.

In the experiment, Kuriba's body was cut up into pieces and the separated human parts combined with mechanical parts to produce two cyborgs. The two lived separately for a year, with data being gathered throughout this period. The set-up meant that data could be collected from every part of Kuriba's body, and being a cyborg researcher herself, she was able to act as both test subject and observer. After a year had passed, she was combined back into one person, with the mechanical parts removed.

The cybernetics used in the experiment incorporated technology which Kuriba herself had developed, including safety limiters which would prevent the cyborg body from performing actions which would damage itself beyond a permissible level, artificial muscles which used chemical reactions to expand and contract, and suppressant materials to prevent rejection from flesh towards the machinery bonded to it.

Doppelganger
Although testing and observing cybernetics and their compatibility with the human body was the experiment's primary objective, the research institution also hoped to observe a side-effect - the creation of a soul (魂の生成).

The idea and question behind this hidden objective (which Shokuhou Misaki described to Misaka Mikoto while explaining the experiment) was that supposing there was a phenomenon known as the soul, what would happen to the soul when the test subject was split into two. As it seemed hard to imagine that one of the two would simultaneously die if other one happened to die while they were separated, it was supposed that when the test subject's body was physically split and made into two cyborgs, the soul would also be split and doubled. With one soul having become two, when the two bodies were made one once more and with one soul residing in it, the next question was what would happen to the leftover soul, with the possibility of it coming to reside in a body made from the assembled mechanical parts left over from the two cyborgs.

After Kuriba Ryouko had lived as two separate cyborgs for a year, she was recombined back into one body and the leftover cybernetics were combined into one mechanical body. The result was what researchers called the Doppelganger (ドッペルゲンガー), a mechanical duplicate of Kuriba Ryouko, who believed herself to be the real one and perceived herself as such, which the researchers considered the realization of their hopes. The doppelganger possessed Kuriba's knowledge, but only possessed memories from since the start of the experiment.

When considering the risk posed by the doppelganger, although not fully convinced about the soul, Kuriba Ryouko theorized that unlike other souls, thought to be linked to the body and destroyed when it ceases to function, the doppelganger's soul was merely stored inside the mechanical body and if the container was destroyed, it would be freed from its restraints and spread to its surroundings. She also theorized that the abnormal "free soul" (自由な魂) would be able to possess anything or possibly, in the worst case scenario, engulf the city itself.

However, shortly after discovering her true identity, the doppelganger came to the realization that she did not have a soul and was just an artificial intelligence. Having predicted the theory which her original would consider, the doppelganger used its calculative ability and assimilated intelligence and creativity to incorporate the theory into its plans. During its attempt to destroy the means to recreate herself and bring about her own destruction, she utilized artificial self-replicating artificial muscles, created from materials at the abandoned Shinasame University DNA Map Analysis Laboratory, which gave the illusion of soul possession (魂の憑依).

The doppelganger and others ultimately concluded that there was no created soul and the researchers' conclusion that one had been generated was merely the result of wishful thinking. However, there was a notable after-effect of the incident. After some of the destroyed doppelganger's parts were placed into Kuriba following her gunshot wound, the doppelganger started appearing in her dreams, displaying knowledge and behavior which only the doppelganger would possess and which Kuriba had no way of knowing, such as that of the doppelganger's battle with Misaka Mikoto.

Facility, Staff and Airship
The research institution which carried out the experiment was based in a skyscraper (which had a triangular gap in its outer cladding around one corner), with its laboratory in the bulbous top floors of the high-rise building. The lab contained the capsules and equipment necessary for the disassembly, reassembly and monitoring of the test subjects, as well as living quarters. An outer corridor surrounded the lab, with windows looking out onto the city. The lower floors of the building apparently had layered security. There were a number of steel banners around the base of the building.

Besides Kuriba Ryouko, who was both researcher and test subject in the experiment, there were numerous other researchers involved on the project, who were aware of and hoped for the other possible product of the experiment. The chief researcher was a man who had initially sought to develop a cheap cyborg method for medical refugees, but had eventually strayed. Another notable member was a female researcher, who was involved in hiring Scavenger to retrieve the escaped doppelganger.

The research institution had an off-site back-up in the form of a catamaran-style airship, equipped with polarizing deception technology to conceal itself. Once a month, the airship passed through a specific location for an exchange of information via laser, but followed random flight paths for the rest of time, such that not even the institution itself knew where it was.

Background
The experiment was devised at a certain institution in Academy City, which had initially had trouble finding volunteers, given its unprecedented nature. Kuriba Ryouko, who was working at the institution in order to develop a cyborg treatment for her mother, ended up volunteering for the experiment to gather the necessary data in the short time she had left. Her body was subsequently split in two and the missing parts replaced with machines to create two separate cyborgs. Acting as both observer and specimen, she planned to use the experiment to gather data on every part of the body. After a year living apart, the two were recombined into one, with no split personalities or rejection, and retaining the memories of the time split apart.

After being recombined, the researchers showed Kuriba Ryouko the doppelganger formed from her combined cyborg components, one who believed herself to be Kuriba Ryouko, and the product of the researchers' hope to observe the creation of a "soul". Although not fully convinced, she warned the scientists of the potential risks, theorizing what might happen if the mechanical body was broken and the created "soul" released. The researchers ignored her, believing the safety measures and security in place to be sufficient and believing that the event of the doppelganger realizing her true identity would merely be an opportunity to gather additional data.

While working on the cybernetics for her mother,   Kuriba tried to find a solution to the problem posed by the doppelganger and the "soul" but was unable to find one. She subsequently spread Indian Poker and some of her own knowledge, in the hopes that it would eventually lead to a solution.

About a month after the recombination, having been kept in the lab under the pretext of observation for after-effects, the doppelganger noticed that she could not recall any memories from before the experiment, and realized her true nature, as well as the fact that she didn't have a soul. She subsequently sought her own termination, but was unable to terminate herself due to safeties built into her mechanical body, so she made a plan to escape from the laboratory, destroy the means to recreate her, and bring about her destruction,  predicting and taking into account the soul diffusion theory which her original was likely to consider.

Dream Ranker Arc
Following the trail of the Indian Poker cards, Shokuhou Misaki learned of Kuriba Ryouko and the experiment she participated in, and shared this information with Misaka Mikoto. As Mikoto was heading to investigate the facility, the doppelganger escaped from the building, destroying its GPS, adhesive restraints and the on-site research data in the process. While Mikoto and Shokuhou visited the original Kuriba Ryouko, the researchers hired Scavenger to retrieve the doppelganger. Meanwhile, the doppelganger, unable to terminate herself due to the safeties built into her, sought to destroy herself and any means that could recreate her, planning to trigger Academy City's interception system against the airship.

The doppelganger subsequently came into conflict with Scavenger and then Misaka Mikoto. During her battle with the latter, the doppelganger threatened to drop gas tanks on the city, forcing Mikoto to intercept them with iron sand bullets. As a result, iron sand filled the skies of Academy City and fell on the airship, resulting in solar wind interference disturbing the magnetism and its stealth, enabling the doppelganger to locate and board it. When the doppelganger eventually managed to convince Mikoto, who by then had realized the doppelganger's true intentions, both doppelganger and airship were destroyed by the massive thundercloud brought down by her.

Arriving afterwards and seeing the destroyed remains of the airship and the doppelganger, the research chief attempted to salvage the remains despite the girls' pleas to let the doppelganger rest, threatening Kuriba at gunpoint to force their cooperation and refusing to believe that the doppelganger didn't have a soul. After accidentally shooting Kuriba in the abdomen as she tried to convince him to stop, he fled the scene and intended to repeat the experiment, possibly using Child Errors. However he was apprehended by Shokuhou using Mental Out. Learning of his original goal before he strayed, Shokuhou decided to help him recall his original intentions and that if he wished to redo things, he would have to crawl back up from below where he started. In the aftermath of the incident, the research institution went out of business.