User blog comment:Miskos3/Fairy Tail Chapter 508: Pleasure and Pain, Review/@comment-86.70.179.73-20161031153436/@comment-4829046-20161101080704

I said 'basic sentiment' precisely because of that. :) I'm still going on him being an artificial entity, but if he was natural, then he could have started calling him Father by his own accord, much like how Midnight did. He might be the first instance of Zeref actively training a child without leaving their development to someone else like say August. Assuming Larcade had his OP magic then, Zeref wouldn't have had to worry about accidentally killing him. Zeref seemed to have taught magic to plenty of people, but only been a mentor/superior figure, not a father figure. Even the Demons do not refer to him in that particular intimate manner despite him technically being their father. Not to mention that not even all biological children are particularly guaranteed to call the male parent 'father' or similar term. Heck, a parent can flat out just avoid acknowledging one as a biological child so Zeref can be uncaring whichever the actual origin.