Anime First: Technically the manga was released first, but it's meant as an advertisement for the anime and was overtaken by it in only a couple episodes (the manga being released on a monthly basis with about the same amount of content per release), so the story is anime first.
Schedule Slip: The series skipped airing for a week in June due to a soccer game, and skipped the first two weeks in August due to the 2012 Olympic Games. Because of the delays, the last two episodes aired on November 19, since Zetsuen no Tempest took over the show's timeslot in October.
What Could Have Been: Allegedly, the series' original writer backed out of the project after only writing the first two episodes, forcing the crew to write up an entirely new plot.
Supposedly, Naru was going to be a member of Pied Piper. Which explains a lot about the original opening, really.