"To Aru Kagaku no Railgun" is set in Academy City, a technologically advanced metropolis where students develop supernatural abilities known as "espers." The story centers on Mikoto Misaka, a Level 5 esper and the third most powerful in the city, who wields the ability to manipulate electricity, earning her the nickname "Railgun." Alongside her friends, including the cheerful and teleporting Kuroko Shirai, the kind-hearted Kazari Uiharu, and the energetic Ruiko Saten, Mikoto navigates the challenges of daily life while uncovering darker secrets within Academy City.

The narrative explores both slice-of-life elements and action-packed arcs, blending personal struggles with larger conspiracies. Early episodes focus on the camaraderie among the main characters, showcasing their interactions and minor adventures. However, the plot gradually delves into more serious themes, such as the ethical implications of scientific experimentation and the exploitation of espers. A significant storyline involves the "Level 6 Shift Project," a clandestine experiment aimed at creating the first Level 6 esper by cloning Mikoto. This arc introduces Misaka's clones, known as the "Sisters," and highlights her determination to protect them while confronting the morally ambiguous scientists behind the project.

The series also features recurring antagonists, such as the enigmatic ITEM group, a team of powerful espers working for shadowy organizations. These confrontations escalate the stakes, blending intense battles with moments of character growth. Throughout the series, Mikoto's relationships with her friends and her moral resolve are tested, emphasizing themes of justice, loyalty, and the consequences of unchecked ambition. The narrative maintains a balance between lighthearted moments and darker, more complex storylines, creating a multifaceted portrayal of life in Academy City.