here.) However, after watching the movie again for a third time, I have to amend my initial theories about Rey's mysterious origins.
I'm now confident that Kylo Ren knows exactly who Rey is.
I came to this realization when a cringing officer informs Kylo Ren that a girl helped Finn and BB-8 escape Jakku. Kylo immediately and pointedly asks, "What girl?" - but it's the way Adam Driver delivers the line that made something click. He's asking because he knows of a special person left behind on Jakku; he knows a powerful girl who, given the chance, would be drawn to a larger purpose by the Force.
Also, in the novelization of the movie, when Rey uses the Force to snatch the lightsaber away from Kylo, he says "it is you". Now I'm not one for putting too much stock into scraps of dialogue found in ancillary materials, but there you have it nonetheless.
A few times in the movie, we see Kylo Ren in a position to kill Rey but he doesn't even think of it.
- Captured for interrogation, Kylo never threatens Rey's life. Yes, he could have shown restraint because he wanted information out of her...but he doesn't seem like the most stable person. At no point do we get the feeling he's going to physically harm her. Something's up.
- In Rey's visions, we see some kind of warrior standing above Rey in the rain, about to kill her - until he is himself killed by Kylo (backed up by the Knights of Ren). This is either a flashback or perhaps a glimpse of the future, but either way, Kylo is saving her life.
- Kylo and Rey have a climactic lightsaber battle, but Kylo's goal is not to kill her, but to break and recruit her. When put in the position to go for the kill, he relents, instead offering to be her teacher.
So What's Going On?
From the above, I conclude that Kylo knows who she is and continually spares her life to some purpose. Why?
Some of my original theory still stands but instead of Luke sending Rey away after the debacle that was his Jedi school, perhaps it was young Kylo who deposited Rey on Jakku. Assuming Rey is his cousin, it's possible they grew up together and he has a soft spot for her. Instead of killing her, he drops her on a planet out at the edge of nowhere to get out of his hair. It might also explain why the Falcon was there: Kylo stole his dad's ship, left it and Rey on Jakku, then took off on the vessel we see in Rey's vision. Maybe he left her there as a backup plan, in case he needed extra help one day, he'd go get her to join forces with him.
But now that Rey's back in the picture, his hand is forced, so he tries to recruit her instead, with the aim of ruling the galaxy as a family, as Vader once tried with Luke.
There's another, nuttier version of this theory where Rey is Kylo's younger sister. Nowhere in the movie is it said that Kylo is Han and Leia's only child.
Who Else Knows?
I think everyone who knew Rey as a child thinks her dead.
Luke, Han, Leia, even Snoke: they all believe the Skywalker girl is dead, so nobody even thinks that she is who she is. At least not at first.
Imagine this: there's a great battle at the Jedi school, Kylo wrecking everything, killing students. But when it comes to Rey, he holds back, kidnapping her instead but making it appear as if she's dead so nobody goes after her. That's when he dumps her on this backwater (back-desert?) planet, out of the way and effectively dead to the galaxy. At the end of the movie, it appears that Luke is standing next to a tombstone. If it is, perhaps it's not for a long-lost wife, but maybe his daughter (or is she his niece?). That would explain the look on his face and the watering eyes: he just came face to face with a ghost, kin he thought killed long ago.
To that end, there's an interesting juxtaposition during the Maz's castle sequence. Han and Maz are alone at a table, and Maz asks "Who's the girl?"; we don't see Han's answer. Instead, it cuts to Finn telling Rey he was taken from a family he'll never know (much like Rey was intended to live out her days), and then the next scene is Rey walking into her vision. These two sequences act as the answer to Maz's question.
So what did Han actually say? I think at this stage, Han suspects Rey is his niece (daughter?) and tells Maz as much. I could only assume that Maz (knowledgeable in the ways of the Force) arranges for Rey to find her way to Luke's lightsaber, to see if it calls to her, to see what reaction she has. It's a kind of test to see if she truly does have Skywalker blood in her veins, a test intended to prove Han's hunch.
But What Do I Know?
But hey! I could be way off base. The fun with movies like this is in the speculation. Fan theories keep interest alive during the interminable wait between installments (I can only imagine the speculation back in the day during the torturous years between ANH and ESB, then especially between ESB and RotJ). Even if I'm completely off my rocker with these ideas, half the fun is in the guesswork.
We've never had flashbacks in a SW movie before, so I'm really looking forward to seeing how they handle all this backstory: break with tradition and have extended sequences in the past, or via exposition. The former is more interesting to me than the latter, chiefly because it would be an excuse to get Harrison Ford back into these pictures.