User blog comment:- Darkchylde/Acnologia's Element?/@comment-173.87.12.242-20141211055642/@comment-7418318-20141214181044

Hmm.... Zeref only gaining "immortality" (or more likely very very long live) due to linking himself with Acnologia's life-force? That is an interesting concept indeed.

I wonder how that would be resolved though if it's the case. Here are a few scenarios that floated into my mind right away:
 * 1) If one dies so does the other. This one I would like the least, since it would take care of one of the two main antagonists "for free" unless they are forced to work together, which I wouldn't like much either.
 * 2) You can only kill them if you deal with both of them at the same time, requiring a concerted effort. Pretty much a lower-numbered recycled version of Nirvana's lacrima, but also a lot more interesting because unlike the lacrima the targets of this linking magic are fighting back, making a simultaneous kill all that much harder.
 * 3) FT will undo this bonding before they deal with either of the antagonists. I have no idea how FT would do that, or even learn of the bond though.
 * 4) Right now Igneel was only able to stand up to Acnologia on his own because the Dark Dragon was weakened by Zeref leeching off of his life-force. Once Zeref is dead or the bond is blocked/disrupted/severed, Acnologia will regain his true power. This carries the danger of cheapening Zeref, but then it would make Acnologia all that much more terrifying.