User blog comment:Omega natsu2/Fairy Tail Zero: Mavis, The Black Wizard, Review./@comment-108.28.233.191-20150120081819

I expect they'll last at least 12 chapters. Zero and Ice Trail run in Fairy Tail Magazine, which is essentially the DVD release of the current run of the anime with some nice extras. A year was planned for that originally, so roughly a dozen chapters would cover the releases. However the anime has been renewed for another year, which may extend their run.