I just downloaded and watched Fairy Tail Episode 101.I get the felling that they have somekind of relationship with each other.The following theories like :They are brothers or Friends.etc make somethings clear.
Natsu and zeref encounter each other, while they encounter the Natsu' s scarf becomes black from white protecting Natsu from Back magic of Zeref.
I get to the things like Zeref is being controlled by Acnologia.He said that once he witnessed many people dying in war. He also became cursed and helplessly started to take the souls of others without his own intention.This explains some curse like acnologia taking control over him.
The next question to be asked by me is about Hades (Second master of Fairy guild).I can get to the feeling that he is stupid to awaken the great magic of zeref without idea and trying to control him.Is not he such a stupid person.
Now let us get back to zeref and Natsu.I am also interested in knowing someone like Gajeel Redfox and Natsu after 7 long years.When it comes to timeskip, it is the second best anime after One piece to have cool controlover it' s timeskip.
Now, what is zeref??Who ia he??Who is Natsu and what is he?? These are the questions implanted in me.I think it will revealed soon.I also need to find out about Zeref and Natsu relationship.You can give any thoeires related to it.Just interested in Fairy tail.