User blog comment:FairyRaven/Fairy Tail Chapter 388: Erza vs. Minerva, Review and Commentary/@comment-25395574-20140617184856/@comment-4829046-20140619115631

Precisely. In other words, it is random a.k.a. unexpected or sudden all the time. Heck I believe the biggest designs that we actually look for are into some powered-up versions like Super Saiyan or Djinn transformation or something. You know, something where we actually want a design change and know full well the author is going to give it? Other than that, any small changes to hair or clothing or even make-up are unexpected or in Minerva's case, sloppy.