Total Human Cyborg Replacement Project

The Doppelganger Experiment (actual name unknown) was a cyborg experiment carried out in Academy City.

Airship
The research institution which carried out the experiment had an off-site back-up in the form of an 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". She warned the scientists of the potential risks, but she was ignored. About a month after the recombination, the doppelganger realized her true nature and 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.

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 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 girl's 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.