Toaru Kagaku no RailGun s is the fourth season of To aru series ( as far how i know ) ( it,s To Aru Index 1 , 2 and there is To Aru Kagaku no RailGun ( this tell,s the back story of Misaka Mikoto ) so before you watch this season you should watch all the other seasons . it has a good Action , Romance and Super human powers ( Easpers ) . i really liked the show Because the Powers and the story development is very good .