User blog comment:Monkey.D.Me/BATMAN Vs. SUPERMAN in ManGotham/@comment-4829046-20130814060924/@comment-7418318-20130814091740

Unless they file lawsuits or start duking it out verbally or textually (is that even a word?) over the internet (twitter, ect...) I would consider any parallels between their stories as coincidence, friendly teasing or homage.

But all the things the two manga have in common are of the rather generic type and have been done by other authors before them. Also if you have stories as long as Fairy Tail and One Piece you are bound to have a few similar things sooner or later.