User blog comment:Miskos3/Fairy Tail 526: My Name Is..., Review/@comment-24039234-20170313110242/@comment-2214433-20170313114044

And so, we go back to the main problem of virtually every arc since Tenrou: good build up, good concept, terrible finale and its execution.

You see, even if the idea of the relationship between Mavis and Zeref was interesting at the start, even if the idea of a child born from their (forbidden?) love sounded like a good start of a story, Mashima just didn't develop it in a way that didn't end up being retarded. It's basically what you said: good material. But that's it. It wasn't used. It was burnt through. Like using high quality wood that could've built a house as firewood.