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.

Finding herself face-to-face with a clone of herself, Misaka ends up helping her get a cat out of a tree, sharing ice cream cones, and having tea with her. It isn't until later that Misaka discovers the true, sinister project that calls for her clones.

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.

Kozaku uses Exterior to make her way into Mikoto's mind, convincing her to attack the building without windows. Before she can go after Gensei, Shokuho must contend with Kozaku's puppet, until help arrives from an unexpected source.

Kamijo and Sogiita find that at best, they can only slow down Mikoto's transformation. Kuroko continues to search for Kozaku while dodging her puppet. Gensei pursues Shokuho for the access code that will let him unlock Exterior's potential.

Gensei has fallen victim to Shokuho's cunning, but Mikoto is still struggling to contain her power. Kamijo decides that he must help her at any cost.

Shokuho and Mikoto find themselves in a traffic jam, and Shokuho demonstrates a tremendous example of her ability. The background behind the Exterior project is revealed, as well as Shokuho's connection to one of the original Misaka clones.

A young Kozaku grins and bears her way through her youth in an Academy City research institution, where she befriends Dolly, one of the other girls there. But when Kozaku learns the grim truth about Dolly, it sets her on a life-altering course.

Frenda and Saten find themselves under fire from an unknown assailant, and duck into a department store to find cover. When none of Frenda's usual tricks seems to work against their pursuer, she has no choice but to resort to drastic measures.

With her closest friends now giving her the cold shoulder, Mikoto feels isolated and helpless, but finds a surprise ally in Kongo. Kongo tries to track down any clues that will lead her to the whereabouts of Mikoto's missing "twin sister."

Misaka lashes out at Accelerator, but is left frustrated. She realizes the full breadth of the situation she has become involved in, and feels responsible for allowing it to happen. Nunotaba discusses the ramifacations of the clones' existence with Misaka.

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.

Academy City's Daihasei Festival is approaching, and the festival's steering committee is charged with recruiting at least two Level 5s to take the athlete's pledge during the opening ceremonies. However, getting volunteers proves to be a challenge.

The Tokiwadai team competes in the Balloon Hunter event, but due to a case of mistaken identity, one of the Sisters substitutes for Mikoto. Yoshio Baba feeds the other school's team with data on the Tokiwadai competitors, with surprising results.

Saten's quest for Shadow Metal ends up landing her in trouble. Uiharu notices something amiss with the website Saten was browsing. Mikoto learns that Wannai did not get her gym uniform returned, prompting her to go track down her Sister.

Saten carries an injured Kongo to safety, while Awatsuki and Wannai tackle Yoshio Baba and his robotic Great Danes. Mikoto spots Saten with Kongo in an ambulance, blames herself for getting Kongo hurt, and determines to set things right.

With Kongo out of danger, Awatsuki finishes the task of having her psychometrist friend probe the kitten's memories. What Saten hears gives her pause, and she turns to Kuroko for advice. Kozaku confronts Mikoto, asking her about the Sisters.

With the assistance of her friends, Mikoto identifies the location from the website data that Uiharu recovered. Upon arriving at the location, Mikoto finds Shokuho waiting for her, and reveals her side of the events that have led up to this point.

Kuroko continues searching for Kozaku, but after exhausting every possible hiding spot in the building, she must reexamine her situation. When Mikoto's transformation hits a critical threshold, it is time for Gensei to unlock Exterior's limiter.

To counter the Doppelganger's giant monster form, Mikoto creates a giant magnetically-induced monster of her own. As the two do battle, it becomes evident that the Doppelganger has an ultimate objective other than combat in mind.

Having realized who Misaka is, Mugino decides to give her a run for her third-place ranking. When Frenda mistakenly leaves her doll-bombs behind while heading to the other facility, Misaka collects them and uses them to supplement her diminished powers.

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.

As the Daihasei Festival begins, Uiharu and Saten enjoy themselves, while Kuroko sees to her Judgment duties. Mikoto and Kongo run an eventful three-legged race against teams from other schools. A plot involving MEMBER begins going into motion.

Kuriba explains to Mikoto and Shokuho how she fears that the Doppelganger's "soul" might pose a threat to the city. The members of Scavenger move in to incapacitate and capture the Doppelganger, but find their task more difficult than expected.

The members of the underworld organization ITEM finish one mission, and are called in to defend the remaining facilities. When Misaka tries to infiltrate one building, she encounters Item member Frenda. Meanwhile, Nunotaba drops in at the other facility.