This is a huge departure from what I normally use this site for, but I haven’t read a guess at Rey’s (from Star Wars: The Force Awakens) back story, or who she really is.
My belief is that she is a Solo. The daughter of Han and Leia, and younger sister to Kylo Ren. To be clear, they aren’t twins, just siblings.
The biggest blow back I get from this theory is why Han didn’t know it was his daughter when they met. It was established in the movie that Han left Leia a lot. This would also mean he left his kids too. We see that Rey was very young when she was left on Jakku, so it isn’t that big of a leap to imagine that Han wouldn’t recognize his own daughter after at least a decade of not seeing her. Not to mention he just got the Falcon back, and is elated by that. He isn’t thinking that he would find his daughter at the same time. To him, the chances of that are greater than Luke making his shot against the Death Star.
But at the end of the film, Leia, who is Force sensitive, blows past her long time friend Chewie and the whole resistance to hug Rey all alone. They focus on this scene quite a bit. JJ likes to keep things secret, and he has gone on record saying that he thought that scene was a mistake.
“That was probably one of the mistakes I made in that. My thinking at the time was that Chewbacca, despite the pain he was feeling, was focused on trying to save Finn and getting him taken care of. So I tried to have Chewbacca go off with him and focus on Rey, and then have Rey find Leia and Leia find Rey. The idea being that both of them being strong with the Force and never having met, would know about each other — that Leia would have been told about her beyond what we saw onscreen and Rey of course would have learned about Leia. And that reunion would be a meeting and a reunion all in one, and a sort of commiseration of their mutual loss.”
Now why would he use the word reunion if they had never met before? We aren’t privy to any of their conversation except their parting words “May the Force be with you”, but they sure do hug for a real long time for people who just met.
There are other things in the film that make me think she is a Solo.
She can understand Chewie. Wookies are rare in the Star Wars universe. So there is no reason why someone from a backwater planet would understand all those howls and growls, unless they knew one of the few Wookies that are free in the galaxy.
She flew the Falcon “solo”. This is pretty epic because it was the first time it has happened on screen ever. And in the expanded universe book Smuggler’s Run, Chewie explains that the Falcon is almost impossible to fly. You have to know it well in order to even get it off the ground. He even says that it NEEDS a co-pilot.
Also, Rey is an amazing pilot like her father, uncle and grand-father. She also has an amazing knowledge of how things work. Not un-like Anakin who made robots and speeders in his spare time as a slave.
Kylo Ren has a crazy obsession with her. Not only does he freak out when he finds out a girl help BB-8 escape, he takes off his mask and shows her his face. I think he did this to see if she would recognize him. And as he is trying to extract the details of the map to Luke he tells her “Don’t worry, I feel it too.” This is an interesting echo to “search your feelings, you know it to be true”. It even rhymes!
The whole flashback scene (it isn’t a flash forward!) lands you right in cloud city where Luke found out the truth about his father. Then boom, we get Kylo marching in with his other knight of Ren and Yoda saying “Its energy surrounds us, binding us together”, so we know she is bound to Kylo somehow. And with all the family imagery, we know they’re closely related.
Then we have all the glaringly obvious similarities to Luke’s up bringing: desert planet, an old family friend lives on the same planet a short droid journey away, and OB1 is there for their first steps.
The book by Alan Dean Foster adds a little bit more to this puzzle when Rey meets Kylo for the first time on Takodana, their conversation is a little longer than in the film. As he has Rey paralyzed by the Force and exploring her mind he says: “So afraid. Yet I should be the one who should be scared. You shot first.” Who is the most famous person in the Star Wars galaxy for shooting first? That’s right. Han Solo.
When you add it all up: Rey is the youngest child of Leia and Han. She was taken to Jakku (most likely by Luke when he banished himself) in secrecy. Not even her parents knew where. This most likely happened when Ben Solo went all dark and attacked the Jedi academy Luke was running. She was left there until the Force decided she needed to be awakened, with only one person trusted with that knowledge, and he got hacked to bits with a laser sword.