User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-4933386-20160808224105/@comment-4945830-20160809020759

Neinhart=No heart. The amount of hearts he has is none. That can also be stated as he has Zero hearts.

Brain died but did Zero die or move on to another host on some possession type magic? Perhaps Zero was a demon or a spirit as opposed to alter ego.

However my theory of Jacobs contract with the Shinigami fell through so doubt Mashima can pull off a good idea such as Zero possession.