User blog comment:IamJakuhoRaikoben/Chapter 452: The Prelude to the Final Battle, Review./@comment-31.132.65.53-20150914233004/@comment-25962249-20150915053847

Zeref got cursed because he was tried to change history by bringing back his brother.

Mavis got cursed because she tried to change history to save a friend by using magic before she fully learned it.