Leader is Leader of Scavenger for a reason: not only is she smart as a whip and good at thinking on her feet, she’s also pragmatic. When the Railgun arrives, she knows there’s no use fighting her or getting on her bad side. Leader has a mission that needs accomplishing, so she tells Mikoto she’s an undercover member of Judgment tasked with retrieving the doppelganger.
It’s fun to watch Leader navigate a virtual minefield with her subterfuge, not knowing how the Railgun will respond to what she says. Luckily for her, she can relate to Seike as a fellow “civilian” aiding Judgment since she does that for Kuroko and Uiharu all the time. Leader also lucks out when she learns Mikoto is big Gekota fan…but is less enamored of Leader’s praise for fellow Level 5 Shokuhou Misaki.
Leader is ultimately successful in getting Mikoto to help her, and it’s a good thing she does, because the doppelganger is far, far beyond the talents of the members of Scavenger alone. She also gets to watch firsthand just how much of a badass the third-ranked Railgun is against such a foe. The doppel, for her part, wants to “level up” some more before properly fighting her.
Leader has Mikoto lure the doppel to a district of abandoned warehouses. It makes sense to Mikoto because that area will result in the fewest casualties, but she asks Leader to evacuate the district of all Skill Out members. Leader wants the doppel in that district because that’s where Scavenger’s contract says to make the exchange with the lab coats. Yakumaru performs a lovely bit of theater convincing a bunch of punks to be chivalrous for a change, helping her warn others to evacuate.
As Mikoto pokes, prods, and analyzes the doppel while air-boarding on a scrap of metal, Leader makes contact with the researchers, and when they quibble about the details, Leader loses her patience. She and her comrades have almost died five times over trying to capture this subject, and their client’s van isn’t going anywhere (thanks to Seike) until their Joan Hancock is on the bottom line of that contract.
But while Leader and crew escapes with the signed contract, their reputation on the mend, Mikoto’s left holding the doppel bag, her sparking hands having become decidedly fuller as the doppel grows to the size of a kaiju. It’s also the case that Leader feels kinda bad about deceiving the kind and well-meaning Railgun, but she’s not loyal to Judgment; she’s loyal to the Dark Side, and to her organization.