User blog comment:FairyRaven/Fairy Tail Chapter 356: Tartarus arc - Prologue, Review and Commentary/@comment-7418318-20131018133926

So Cobra tries to get OS out of prison.

That somehow gave me the feeling that Yukino will die and Angel will pick up her keys to fight Tartarus with them.

And a few chapters before the end of the series, she will pass them on to Lucy.