Mikoto Misaka and her friends return to Academy City and embark on a mission to uncover the truth behind chilling rumors. Their investigation reveals numerous gruesome experiments taking place throughout the city, resulting in the deaths of countless espers. Shockingly, these espers are not ordinary humans, but rather clones created from Mikoto's DNA. Fueled by guilt and responsibility, Mikoto attempts to put an end to these studies, but her efforts are met with fierce resistance from formidable adversaries. This is the story of Mikoto's journey in Toaru Kagaku no Railgun S, as she struggles to make amends for her past mistakes while grappling with escalating emotional turmoil. Life in Academy City is not always joyful, and its relentless nature continues to unfold.