A Certain Scientific Railgun

Thwarted in her attempt to sabotage Tree Diagram, Misaka takes her frustration out on a nearby lab that is part of the project. Meanwhile, Accelerator and #10031 carry out their experiment, while Kamijo searches for Misaka's missing sister.

While Shirai frets about Misaka staying out again all night, she receives a visit from Kamijo, who manages to find Misaka's documents about the project. Kamijo catches up with Misaka on a bridge, where he tries to talk her out of doing anything rash.

Kamijo races to the scene of the experiment, only to find that it has already started. Kamijo calls out Accelerator, who takes him to be yet another challenger to his position, until for the first time, as Misaka watches on, he gets his nose bloodied.

Misaka stands up for clone #10032, declaring that she is doing so because they are sisters. The next day, the two of them spend time in a park, where 10032 asks her for a special favor. Later, Misaka has difficulty trying to express her thanks to Kamijo.

With the end of summer vacation approaching, the girls plan a study session at Saten's apartment to catch up on homework. Everyone is to bring an ingredient for a potluck stew party, but most have trouble deciding what to buy, leading to some surprises.

Edasaki is due to be discharged from the hospital, and it is learned that she will be living with Haru'ue. The move is bittersweet for Uiharu, who is losing her roommate, but she feels it is for the best. Meanwhile, a new movement is afoot in the city.

Febrie takes an instant liking to Saten, and is warm to everyone except for Misaka, much to her chagrin. At Judgment, Uiharu is unable to find any information on who Febrie is, so arrangements are made to admit her into an orphanage as a "Child Error."

As Yomikawa takes over investigating the runaway security robots, Konori invites the whole gang out to take in a bath at a bathhouse. On their way home, a number of detours lead them to a confrontation with yet another, much more dangerous runaway robot.

With the revelation that Febrie is synthetic, Misaka is determined to find whoever built her, and have them fix her. The investigation is stalled on all fronts, even with the help of her friends running down leads, until help comes from a surprise source.

Therestina reluctantly provides Misaka with the clues she needs to find the group behind Febrie's secret. With Kongo's help, the girls identify Aritomi as the man they are pursuing, and find out more about him and his company, the STUDY Corporation.

Aritomi reveals his motivations for STUDY's project to Misaka. She also learns about Nunotaba's plight, and some of the details concerning what STUDY has planned at the Reach Assembly the next day. Will she be able to escape and put a stop them?

Shirai, Konori, Kongo and friends, and Uiharu and Saten confront the powered suits at the four Assembly sites, where they soon receive backup. Misaka and Febrie move to take on Aritomi directly, but he has one final surprise up his sleeve for them.