Toaru Majutsu no Index Episode 10

Synopsis
A girl resembling Mikoto Misaka wearing military goggles uses a sniper rifle to shoot a teenager called "Accelerator", only for the shots to be reflected back and her to wind up face-to-face with Accelerator. Tōma runs into Mikoto Misaka and, after learning of how he defeated her, expects the worst until she is caught off guard by Kuroko Shirai, Mikoto's kohai who soon teleports away, and then by another girl who looks exactly like Mikoto and identifies herself as Mikoto's younger sister, referring to herself as simply Misaka. Frustrated, Mikoto leads Misaka away despite Misaka’s objections, though Misaka approaches Tōma later that day and helps him carry tin cans. At summer class the next day, Tōma, Tsuchimikado, and Aogami learn that Mikoto became the third most powerful esper in Academy City from Level 1 to 5 through hard work and effort while Mikoto later tells Tōma how she dislikes Tree Diagram, a powerful supercomputer on a space satellite that monitors Academy City. As soon as Mikoto leaves, Tōma runs into Misaka again, who wants to care for a black cat. As Tōma leaves her to find books on caring for cats, Misaka senses Accelerator nearby and a fight ensue in a back alley.

Adapted From
Adapted from? which chapter of manga and/or novel

Referbacks
references to previous episodes

Animation Trivia
Around the 10min 39sec time frame, Misaka puts the night vision goggles on but then has them in her hand in the next scene, and the back on her head in the next.

New Characters
Accelerator

Misaka sister.

New Abilities
Redirection - Accelerator

Cultural References
"easter eggs"