Toaru Kagaku no Railgun SS: Liberal Arts City is a story written by Kamachi Kazuma, released in parts in the limited edition DVDs and Blu-rays of the first season of the Toaru Majutsu no Index anime. The story consists of eight parts, and can easily equate to a regular Index novel in length. The individual parts were later collected into Toaru Majutsu no Index: Gaiten Shoku Light Novel Volume 02 alongside Toaru Kagaku no Railgun SS2: Shopping Mall Demonstration and Toaru Kagaku no Railgun: Cold Game.
The story is set in Liberal Arts City that takes place in the time period between September 3rd to 10th. Academy City have a exchange program with the rest of the world that allows some students to travel for this week to other places, and some students are allowed into Academy City during this time. Among these students are the third-ranked Level 5 Misaka Mikoto and her friends, Shirai Kuroko, Uiharu Kazari, and Saten Ruiko. However, the floating city ends up having unexpected guests in form of the Return of the Winged One Magic Cabal.
- A special chapter of the Toaru Kagaku no Railgun manga was used to promote this side-story, revealing a few details about the settings and events.
- It is shown that Mikoto can use water to create wings and fly, using one pair for propulsion and another two, smaller pairs for navigation.
- This series of events is what leads to Xochitl's conflict with Etzali in Volume 15, and Tochtli's fate as a puppet in Volume 19.