User blog comment:BlackWizardZeref/Fairy Tail Chapter 399: Wings of Despair Review/@comment-24053170-20140910175513

And now we know how Frosch is going to die, and why exactly rogue swore to kill Acnologia, as well as why he was unable to protect him from being killed. Since Acnologia is most likely the one responisble for frosch's death.