So.. how'd he nullify stuff without his Right hand then?

After rewatching episode 9 of the Index story, none of them had an explanation as to why there was a dragon in his arm. :/ You could be right though, sounds a little odd though for an explanation considering the circumstances. I'm just being picky though, forgive me.

Back on topic. Judging from the story, this takes place before Index, but leads up to the point of Touma meeting Index or is this Story Arc centered on Misaka only?