Big Sister (Mikoto Misaka).A girl resembling Mikoto 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 at a vending machine and, after learning of how he defeated her, expects the worst until she is caught off guard by Kuroko Shirai, Mikoto's kōhai, who soon teleports away, and then by another girl who looks exactly like Mikoto, identified as Mikoto's younger sister and referred to 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 ensues in a back alley.