Does Hiro Mashima (Fairy Tail) have something in common with Eiichiro Oda (One Piece)?
I have read that Oda and Mashima are good friends. However, not only has Mashima never been Oda's assistant, but he has never been an assistant to any mangaka. The resemblance of their artwork is due to something they share in common: Toriyama worship and obsession with Dragon Ball. More details on this blog post.