Yet another Madame X identity theory...

[Gen5Lover]

(english isn't my first language, so there may be errors)
We all know that Madame X identity is a big mistery, and while I don't know if it's 100% provable, I'll lay out my opinion.
No, I don't think that Madame X is Melia, let's get that out of the way. Personally I think that's been ran into the ground at this point.
My theory is that Madame X is actually another Erin. To be more specific Erin from the same universe as Maria/Marienette. That would explain that prolouge at the beggining of the game.
Physical appearence:
Okay, I admit Erin and Madame X (from what we see of her face) don't look nothing alike, but so doesn't anyone of the characters. Tho red eyes are often used as a sign that someone is using some sort of dark magic. Her armor and/or sword have probably something to do with Garufan Magic, seeing how powerful they seem to be. As for black hair, it could be Garufan Magic again but it could be just Erin dyeing her hair, since she does it in normal timeline too.
Personality:
Madame X is a villian, that much is obvious so her mind ain't in the best place. Same goes for Erin. While Erin often acts tough we see that from her talk with Maria she wan't, or still isn't in the best place mentally. What I'm trying to say is that someone like Erin who is brooding then someone cheerfull like Melia.
Reasons:
We all know there is another Erin. Alice and Alen mention they had another sister, Eriana. And if you know something about other versions of characters the one thing that seems to be constent is that they have similar names. They say that Eriana was trapped in Unown Dimension togethere. And yes I do think that Alice, Alen, Eriana and Maria are all siblings. I have some theories on why that may be the case but that's not important for now. Madame X also mentions her father and how she disappointed him, which if we follow this theory makes Indriad her father, an evil man who is known for being evil maniac that uses Garufan Magic and is also a terrible father, also Alice and Alen have a terrible father too. We know that Melia and Erin are somehow connected to Alice and Alen since they four form The Archetype symbol. For why Maria and her mother don't think anything is missing when by this theory they should know about it, it can be number of reasons, probably something like memory deletion, and since Indriad's right hand was a Gardevoir, a pokemon with powerful psychic powers, memory deletion doesn't seem that unlikely. But why would he do something like this? Simple, he has no use from rest of them. Maria just like Melia has light inside her, something Madame X is after. And Madame X having same goals as her father who she seems to think a lot about wouldn't be too strange. Madame X most likely doesn't have same light. For Alice and Alen I don't know if they have since well they did made The Archetype, they never went shining even when they almost died at Grand Dream Ball.
And that would be it, I think. I might have forgotten something but I think wrote enough, if I remember anything I'll add it in comments. Everyone is welcome to debate here about it and give their opinion.

[ParadoxPotentia]

I'm pretty sure you're wrong, and that Erin got 

Spoiler

Dragged/kicked out of the unknown dimension before Alice and Allen, meaning Erin and Erina are the exact same person. After all, Erin is adopted, and their memories were screwed up in there too.

She also doesn't resemble Erin at all, so if you make the assumption in the spoiler, there's no reason to assume she is another Erin. (Besides, all the characters could wind up in a bad mental space in a bad timeline. No one was exactly a bastion of stability in the "sacrifice-less" future.) That said, it is very likely- given that she's got a Time Gear or an equivalent ability- that she is from an alternate timeline, or from this one's future. If we assume that, we can also assume that anyone who has canonically touched her isn't an alternate Madame X. ...but that basically just means that Madame X is not Sakitron, given that she's wearing an outfit that covers literally all of her.

 

We don't have enough evidence to do more than throw wild guesses out, and your theory discards the most useful piece of info we have to narrow down the possibilities. (Honestly, I think the most likely guess we have right now is "She's Nim, either an alternate or temporally displaced", but that one doesn't seem all that likely either.)