When Scavenger is hired to recover Kuriba Ryouko’s doppelganger, they’re upbeat confident they can get the job done, despite having suffered a humiliating defeat in the Accelerator spin-off that I ended up skipping. In fact, Naru (the one with pink hair) sees this “small” job as a stepping stone to regaining credibility among the Dark Side organizations.
The real Ryouko tells Mikoto and Misaki about the dangers of an “untethered soul” of the kind residing within her doppel. It can possess and control any material it pleases and even spread across all of Academy City if left unchecked. She also started the Dream Poker fad as a kind of crowdsourcing for a solution to dealing with the doppel’s soul.
When Ryouko leaves, there’s a bit of tension, as she urges Mikoto not to get involved, but she soon wonders if turning away the Railgun was the right move. In fact, she immediately regrets that when the doppel confronts her, easily chases her down, and promises to erase her existence; clearly the doppel wants to be the only Kuriba Ryouko left standing.
Ryouko is able to use a stun grenade-like device to break Ryouko’s hold and create a smokescreen that allows her to flee. Ryouko would have surely given chase immediately provided she knew which way to go, but she is confronted by Scavenger, who keep her occupied for the rest of the episode.
I’ll give this to the members of Scavenger: they seem an organizaed and competent team under usual circumstances; unfortunately for them there is nothing usual about the doppel. Leader is able to locate the doppel with the Predator skill, while Seike (who is apparently a boy) is able to manipulate friction; between him and the doppel it’s an all-barefoot fight.
Rounding out the group is Yakumaru (an expert in various chemical and explosive agents) and Naru (who can manipulate paper). The four are able to not only stop the doppel in her tracks but restrain her as well. When Leader noticed a second Ryouko flee the area, she sends Seike after her, wrongly assuming the doppel is under control.
The doppel grabs Leader and twists and breaks her wrist. This leads Naru to enter her next-stage “rabbit mecha” form (in which she’d be buck naked but for a few scraps of paper) to separate the two.
The doppel is damaged (which wasn’t part of the job) but unfazed, and uses the power of the soul within her to basically steal Naru’s paper, ripping off an arm of her rabbit mecha and grafting it onto her damaged area.
After their meeting with Real!Ryouko, Misaki shows Mikoto the girl’s memories, and Mikoto learns that she was both researcher and subject in being cut in half as part of her lifelong effort to save her mother, who took a turn for the worse after donating a lung to Ryouko.
With a better understanding of Ryouko’s intentions and motivations, she ends up tracking Ryouko down again, which is fortunate for Ryouko, as Seike tracks her down first and roughs her up a little, just because he can. Enter Mikoto, whom Seike initially doesn’t recognize as the Railgun due to her a sorta-disguise.
It doesn’t take long for him to learn who he’s dealing with, and before sending Ryouko off to safety, Mikoto officially offers to help her with her problem, and Ryouko accepts, thus righting the wrong of their first meeting.
Now armed with part of Naru’s mecha, doppel prepares to crush Yakumaru’s head, but Naru is able to regain control of enough of her paper to stop Ryouko in her tracks, enabling Yakumaru to toss an explodey device that allows Scavenger to flee and regroup, battered but alive.
After making quick work of Seike, Mikoto proceeds to confront Leader, Naru, and Yakumaru. Considering this group already had an ill-fated encounter with the Accelerator, Leader was sure the chances of them coming afoul of another top-ranked esper to be infinitesimal.
Alas, now they have to deal with the Railgun. My advice to them is to surrender peacefully and avoid the same unpleasantness Seike endured. Perhaps they’ll end up joining forces to restrain the doppel…or perhaps the doppel, like Mikoto, is simply out of Scavenger’s league.