I was thinking that what could have Jellal done to Kagura that she hates him that much. As far as i know, in the manga the only people who he had manipulated and deceived (while under Ultear control) are the Magic Council members and the people at the Tower of Paradise.
From what i understand, Kagura seems to be more of an high class/society person, so that takes away the chance of her being in the ToP. Also if she was there then Erza or Millianna would have known her.
So the only answer i get is that maybe she is actually related to one of the former members of the Magic Council (the ones who agreed to fire the Etherion on ToP), and maybe he was actually engaged to her during his time as a Council Member. But with the incident of the ToP, she faced a lot of humiliation along with the person from the Magic Council and now has decided to take revenge on him.
I feel this because it seems Mashima-Sensei does bring up things from the past out of no where. And this seems like a valid options to use.
On another hand i feel that the unknown person Jellal was following in ch 289 might turn out to be Simon (the only thing that counters this point is that the person seen wasn't that tall like Simon). I mean in the whole manga story so far Simon is the only good guy we know has died in the normal time-line (the other good people we have seen die are in the flashback sequences).
Also we aren't really sure about his death. I mean we known that he was hit full force with a powerful spell but was it enough to kill him. Maybe he like Jellal went into a comatose state.
I get the feeling that maybe the real Zeref found him and now Simon is working with him. Thats because we aren't actually sure whether Zeref was really a Evil Mage like the legend say. We only know that he had killed a lot of people but for what. So, maybe after known the truth about him he has started to work for him.
Or else Simon was affected by all that Etherion energy so the feeling of his power is similar to that of Zeref (Simon was a Dark Mage to begin with). I mean Jellal himself said that the person had magic power like but yet unlike Zeref's.
Well if Simon does turn out to be alive, then Erza wouldn't have to face Millianna's side of the problem. I mean she would be angry at Jellal but now that Simon is alive she would at least be ready to hear out Erza (or else she wouldn't).
