If A Certain Magical Index is a wild, unfocused exposition of superpowered fantasy, then its spin-off A Certain Scientific Railgun is a slightly more grounded work that mixes in character development and an actual plot. I’ve always preferred Railgun to Index for that reason – superpowers are more fun when you care about who’s wielding them. The continuation, A Certain Scientific Railgun S, takes the same approach as the first season but moves away from the mostly lighthearted feel of the original.
As a spinoff of A Certain Magical Index, A Certain Scientific Railgun follows the daily life of Mikoto Misaka in Academy City. Being a self contained environment for the study and advancement of espers, life in Academy City is rarely mundane. The excitement picks up as a string of crimes breaks out, all involving espers abusing their powers for whatever reason. Being the roommate of a Judgment member, Mikoto gets drawn into their investigations and peacekeeping activities.
In Academy City, people from all walks of life gather to develop and study esper powers – abilities that seem to defy the laws of physics but still operate on scientifically quantifiable principles. Those who are unable to use esper powers turn to magic, but magicians are strictly prohibited from entering Academy City. This balance is upset when by chance, Toma Kamijo meets the English Church’s most precious magical asset: a girl named Index. Her presence in Academy City attracts other magicians, and Toma has the unlucky duty of having to ensure that the magicians and espers don’t all end up killing each other.