Irene is the thoughts, Erza is the real body...But wait. I am confused. So who is the manifested thoughts and who is the real body here?
It's like....when you have a trauma of sorts? Or a bad experience with something..and you're trying to move on..
That's essentially what Irene is right now, so Erza is a painful reminder of her past..
Does that make sense?


And I also think that the moment Acnologia will kill or at least will make deadly wound to the Irene, something will happen. Either Erza will get flashback of memories or the thing You've proposed. I'm also wondering why Irene herself never went to Erza, she just sending people to kill her, yet she didn't have problem with punishing Mira in person.


