At Chizumatic, Steven remarks in the comments,
“The potential present in the premise about Index is intriguing, but if it were fully developed she’d be too strong, too overwhelming.”
Indeed. In The Dresden Files, (series) the author takes the concept and runs with it in one book. With a small girl, no less. (I wonder if he was reading the manga….) And yes, she’s insanely powerful; she holds off three major demons with ridiculous ease. They only defeated her by luring her into a trap that cut off the flow of magic; once she exhausted her innate supply, she was vulnerable.
(Posted this bit of nothing here, since Steven doesn’t like sidetracks)
In any case, I’m downloading the season, and will give it a second chance; apparently it finishes strongly with an arc about the Railgun. Which I’m still following that series, and Kampfer. Don’t ask me why I’m still following Kampfer.