A Certain Scientific Railgun is a spin-off of A Certain Magical Index. It’s set before and during Index season 1. Season 2 of Railgun is currently airing in Japan and is set during season 1 of Index (it features the same arc from a different prospective. Index features Touma and Index as main characters while Railgun features Misaka as the main character. Railgun season 1 seemed more slice of life and filler-ish as compared to the action in Index.
Anyhow FUNimation only released this on DVD same as with Index, but thanks to the sync efforts of Shiro; we offer you a dual-audio 10-bit 720p encode using the Japanese Blu-ray.