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. Toma 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 Toma later that day and helps him carry tin cans. At summer class the next day, Toma, 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 Toma how she dislikes Tree Diagram, a powerful supercomputer on a space satellite that monitors Academy City. As soon as Mikoto leaves, Toma runs into Misaka again, who wants to care for a black cat. As Toma leaves her to find books on caring for cats, Misaka senses Accelerator nearby and a fight ensues in a back alley.