The To Aru Kagaku no Railgun side story is based on Kamachi's original story set in Academy City, a city where about 80% of its 230,000 citizens are students. The story deals with the adventures of Misaka Mikoto, one of the Level 5 psychics in the To Aru Majutsu no Index light novels
The anime that related on "To Aru Majutsu no Index" but it's not a second season!!
This anime has a main character which is a sub-character from "To Aru Majutsu no Index". But why this is not a second season of that? Because time-line is this story is in the same with that one. While Touma & Index doing those thing in their story ,Misaka is doing her thing in her story ane some time they meet each other!!
I think this idea is very good because when I watch some anime, I ever doubt that what happen to other character. And this anime can answer me those question.
This Anime is the same as "To Aru Majutsu no Index" , has a good animation & character design but I think the story is more interesting than other one.
The Action scene is superb but the bad point is some part is hard to understand for child because its contain theory about scientific and quantum (which some adult still not understand).