There's no fighting game for the A Certain Magical Index/Scientific Railgun series, and there really needs to be. I mean, the closest thing we have to this is a fighting game called Dengeki Bunko Fighting Climax, which is currently only available in Japan in Akihabara, with a possible console and/or PC port on the way, which hopefully will make its way over to the States.
(This game has the 2 main protagonists, Touma and Misaka, as playable characters.)
Still though, we need a fighting for these 2 series (they're set in the same universe). Both parts of the universe bring forth excellent characters that would make for a great fighting game. Make it so game developers, and you will have all of my money...er well...all $50 of it.
-
[spoiler]I just spent five minutes going through my yuotube history to find the crossover fighter to show you, only to read more than the title and find out you already know about it...[/spoiler] I don't even like fighters, but i'd buy a game like this day one.