User blog comment:FairyRaven/Fairy Tail Chapter 365: Fairy in the Jail!, Review and Commentary/@comment-13876472-20131228153322

Erza has been captured by anti-magic cuffs. Since her armor is a product of her magic (I think) could fade out in these cases. Also, if I was planning to torture a person, I would find really annoying to torture him over an iron armor, which is made to mitigate damage.

I don't want to support Mashima's choice to increase ecchi in Fairy Tail. I just want to say that there is some reasoning on it.

To be clear, I really believe Mashima understands that since he cannot offer a good story to the fandom, he can only increase the readers of his manga by these ecchi scenes. A lot of mediocre mangakas did exactly the same to keep their salaries anyway, and they succeeded.