Daihasei Festival Arc (Railgun)

The Daihasei Festival Arc is a story arc in Toaru Kagaku no Railgun.

It is September 19th, and the time has come for Academy City's annual Daihasei Festival, a sporting event that pits ability users from across the various schools of the city against one another in a series contests. For Misaka Mikoto, this year's festivities have come with a twist as she finds herself having to foil a plot that could allow Kihara Gensei to cause great damage to the Exterior of Shokuhou Misaki and to the Misaka Network.

The arc marks the 2nd time that Kihara Gensei acts as the primary antagonist for Mikoto, it involves Kihara Gensei allowing Kouzaku Mitori to confuse MEMBER in order to get their aid in finding the Sisters and Exterior.

This story arc presumably takes place after the Daihasei Festival Arc in Toaru Majutsu no Index as Kamijou Touma is heavily involved in both and they do not appear to take place concurrently.