I will rewatch the RailDex series... It been a while and two new parts are coming this year and I still didnt watched the third season of Index So about the watching order I read an interesting post on another website that I will quote here : Watching the Sisters Arc first in Index absolutely ruins the emotional impact you get from seeing it from Misakas perspective while providing absolutely no gain. The Sisters Arc is 4 episodes in Index and 14 in Railgun S as such the Railgun S versions enjoyment should clearly take priority especially considering the fact that it is the primary arc of the entire Railgun series and arguably the best arc of the entire show. Interesting nonconventional watching order recommended: https://anilist.co/anime/6213/ACertainScientificRailgun/ https://anilist.co/anime/16049/ACertainScientificRailgunS/ https://anilist.co/anime/4654/ACertainMagicalIndex/ https://anilist.co/anime/8937/ACertainMagicalIndexII/ Raildex is a situation where the conventional wisdom of watch it in production order kind of breaks down because there are actually two parallel productions involved. Since this watching order does still preserve production order within each individual production I think it works. If you do watch the series in this order note that episodes 1014 of Index season 1 are basically a condensed crappier version of episodes 216 of Railgun S. Itll be a bit of a slog to get through but you should do it anyway because the Index version shows events from a different characters perspective Toumas. The released order: I dont include the movie and the OVA. https://anilist.co/anime/4654/ACertainMagicalIndex/ https://anilist.co/anime/6213/ACertainScientificRailgun/ https://anilist.co/anime/8937/ACertainMagicalIndexII/ https://anilist.co/anime/16049/ACertainScientificRailgunS/ https://anilist.co/anime/100185/ACertainMagicalIndexIII/ https://anilist.co/anime/104463/ACertainScientificAccelerator/ https://anilist.co/anime/104462/ACertainScientificRailgun3/