Historia
The second season of Toaru Kagaku no Railgun. Something sinister is going on in Academy City. The shadows are filled with whispers of an organization cloning super-powered students known as espers. High-ranking master of electricity, Mikoto Misaka, laughs off these stories until she comes face to face with a copy of herself. After learning that these clones - her sisters - are being systematically murdered in a series of experiments designed to turn a sadistic killer into the strongest esper in history, Misaka vows to save her copies and destroy the organization responsible for the project.
Sinopsis vía AniList (en inglés).