"To Aru Kagaku no Railgun" is a manga series 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 with the ability to manipulate electricity, earning her the nickname "Railgun" due to her signature attack. The narrative explores her daily life, friendships, and the challenges she faces as one of the city's most powerful espers.

Mikoto is a student at Tokiwadai Middle School, a prestigious institution for elite espers. Her close friends include Kuroko Shirai, a teleporter and member of the Judgment organization, which maintains order in Academy City; Kazari Uiharu, a tech-savvy Judgment member; and Ruiko Saten, a non-esper who provides a grounded perspective on life in the city. Together, they navigate various incidents, ranging from mundane school activities to high-stakes conflicts involving criminal organizations and unethical experiments.

A significant subplot involves the "Sisters" arc, where Mikoto discovers that her DNA was used to create clones as part of a clandestine project aimed at advancing esper abilities. This revelation forces her to confront the darker aspects of Academy City's scientific endeavors and her own role in the experiment. The arc delves into themes of identity, morality, and the ethical implications of scientific progress.

The series balances action, mystery, and slice-of-life elements, showcasing the dynamics between Mikoto and her friends while exploring the broader implications of living in a society where science and supernatural abilities intersect. The narrative frequently intersects with the events of its sister series, "To Aru Majutsu no Index," providing a deeper understanding of the shared universe and its interconnected characters. Through its engaging plotlines and well-developed characters, "To Aru Kagaku no Railgun" offers a compelling exploration of power, responsibility, and the human condition within a futuristic setting.