This is a theory that many may call outlandish for some parts, but bear with me and read through all of the arguments for it, and you may start to see why it is a huge possibility.
This theory is based around Kylo Ren and Rey, and their pulls to the light and dark sides of the Force.
I will start off with what I believe is the biggest game changer in the theory, one that states that Kylo Ren is either working against Snoke, or is on the path to the light side of the Force.
What if Kylo Ren joined Snoke in order to bring him down from the inside? What if, knowing he would have to lose himself to do it, Kylo Ren is acting in a charade in order to get close enough to Snoke to kill him, and to bring balance back to the Galaxy? Here are the reasons I think this theory has merit, and why it is a huge possibility for the next few episodes of Star Wars to continue in that direction.
First off, let's look at Kylo Ren's obsession with Darth Vader. Kylo Ren is seen talking to the charred helmet of Darth Vader, telling him that he is constantly feeling the pull to the light, and that he would finish what Darth Vader started. This has always been a very confusing piece to me, because what exactly did Vader start that Kylo needs to finish? Is it the ruling of the galaxy? Because that was what Palpatine started, and not Vader. Was it the destruction of the Resistance? Because that may be a reason, but that seems like insignificant goal considering later in the movie they know the system they are hiding in, and on top of that, have a weapon to destroy them all. To compound off of that, Kylo didn't want to use that weapon against the resistance (stated in the novelization), and he seemed unchanged when he learned that they had found the system to destroy in the first place.
What could he have wanted to finish? If we look at this from another perspective, what was important thing was Darth Vader known to have started? The one answer that I can come up with is to bring balance to the force. Now, we don't know how much Kylo knows about Darth Vader turning to the light before dying, but we do know is that Luke trained Kylo. I highly doubt Luke would ignore the sacrifice of his father and just tell his students that Darth Vader was bad until the end. Luke wanted to save his father, and to keep him memory alive, he probably would have told his students about the sacrifice Vader made, as well as used it in a lesson on how even the darkest minds can be brought back to the Light. To touch more upon the helmet, how did it come into Kylo's possession? I believe that Luke held onto it as a relic, and kept it at his Jedi temple as a reminder of his father's sacrifice. I also believe that before leaving, Kylo took it with him as a reminder that no matter what he does to take down Snoke, he can always be redeemed.
While talking to Vader's helmet, Kylo also mentions that Snoke can sense the pull to the light that he is experiencing. As we have seen with Sith before, there really is no pull to the light unless it is connected to a loved one causing them to experience remorse. Even Anakin felt no remorse with Padme, and continued down his dark spiral. The only thing that we know a true Sith (or dark Jedi, for those who don't like calling the dark side users Sith) is their lust for power. Kylo does not seem interested in power at all when we look at his goals. So what is he really working towards?
To add on to the evidence that Kylo has not succumbed to the Dark Side, lets look at what Leia said about it: "There still is light in him. I know it." We know Leia can use the Force to an extent, since we see her feel Han die and know she is a Skywalker, and Luke himself had the same power to sense the Light Side in his father, so I would like to go on record and say that what she is sensing is truly the Light Side in Kylo Ren.
Let's also look at the Force powers that Kylo uses. The Sith have their own powers that they display on multiple occasions that Jedi would never use. Force lightning being one of them. Now, we could guess that maybe he isn't proficient enough in the Force to use it, but look at what he can do. He can extract information straight from a person's mind. If he can master an advanced technique such as that, why can he not channel force lightning yet? We also have to take in account, though he does choke someone at one point, he did not use the force to choke him the way Vader would, nor did he kill him (At least that we saw). Kylo always takes out his aggression on inanimate objects. Many people call it a temper tantrum, but what if that is really him trying to control his Dark Side urges and stay on the Light path? He could easily just kill the messengers like Vader would have, but he refrains from it.
Let's look at some plot points now. Kylo Ren is obsessed with finding Luke Skywalker. While he is obsessed with finding him, Snoke and Hux seemingly only want to keep the Resistance from finding Luke. They are more concerned with destroying BB-8 than actually capturing him. Only Kylo wants to find Luke. Why would that be? Does he think he is powerful enough to kill Luke? Maybe he is trying to find Luke first to reach out for help, or to tell him the time has come to implement a plan to take down Snoke together.
Now let us look at his mind extraction that he attempted with Rey.
The first thing we see happen is Kylo accusing Rey of wanting to kill him. She responds that "That's what happens when you're being hunted by a Creature in a mask."
Upon hearing this, with no obligation to do so, Kylo Ren takes off his mask for Rey. Why would he do this if not to show her that he is not some sort of monster, and that he was still a man?
Upon probing her mind, Kylo speaks out loud what he is seeing, and when he sensed her loneliness, instead of mocking her, he seemed genuinely sympathetic to the visions he was seeing. Not only that, but this seemed to be a very gentle version of the probe, considering Poe Dameron looked as if his mind was being torn out while being probed. Was he being more gentle on purpose?
When Rey finally peeped inside of Kylo Ren's mind, she say that he was afraid. I think there was more to that than they led on in the movie. Maybe he was afraid he wouldn't be as powerful as Vader, but in what sense? Powerful enough to fight the Dark Side when the time came? He also rushed out very quickly. Was he afraid his plot against Snoke may have been seen if she dug further? Maybe he was afraid of more than not being powerful enough.
Let us also take into account, that Kylo was sounded as if he wanted to stop the destruction of the Resistance system when talking to Snoke, saying he could get the map. He just needed guidance.
Now onto the biggest, most important parts of this theory:
When Kylo Ren and Han Solo meet on the bridge.
It is known that Kylo Ren could sense Han Solo, but as he walks past him in the Oscillator, he completely walks by as if he did not know his father was present. I believe he did not want to have to face what would come next when he did. He walked to the center of the bridge, and Han calls to him. He tells him to take off the mask, to see the face of his son. At this point, we can tell Kylo is conflicted, because instead of ordering Han's death from the stormtroopers around him, Kylo takes off his mask and allows Han to approach. Now, Kylo has been told by Snoke that to embrace the Dark Side, he must kill Han Solo. Kylo obviously does not want to do this.
Han tells Kylo that he will be crushed by Snoke when he is done with him, and Kylo responds with "It's too late." Kylo knows he can't turn back, but he also knows that Snoke is only trying to use him as a pawn in a great scheme. When Han tells Kylo that they miss him, he is obviously very crushed inside. You can see only sadness and remorse for what he has to do. His only choice to stay on his path with Snoke is to kill his father. He tells Han that he is "Being torn apart" and that he wants to "Be free of this pain." Does that sound like someone who is just out for power and greed? It seems to me that he would take any other option that would be given to him. Kylo DROPS HIS MASK before handing Han Solo the lightsaber. At this point it is important to watch how he is handing over the lightsaber. He is handing it to Han's dominate hand, where Han would have full control. He asked before that Han help free him from his pain. Could it have been a cry for help, that Han end the misery he is under that he endured to keep up his dark side charade?
We see the light fade, and Kylo, realizing he will be the last hope to defeat Snoke, kills his father.
What is interesting here is that he says "Thank you," as if he knew it's what needed to be done, and he was thanking Han in advance for a sacrifice that could save more than he knew.
Now we move on to the next part. The battle of Kylo against Rey and Finn.
Kylo is obviously very upset at Finn, but they only have the line "Traitor!" come out of his mouth. Is he upset because Finn defected from the empire? Because of all people who have been traitors up to this point, Kylo renouncing his roots and killing his father would make him the biggest. Maybe, instead of being mad at Finn for leaving the order, he is regarding Finn as the traitor for leading Han there to his death. The moment Finn co-opted the mission, Han's fate had been sealed. I think it's entirely possible that Kylo was so angry for that reason alone. If it wasn't for Finn, Han would have survived. Another big point I would like to discuss is his emotional need for Luke's lightsaber. Why did he want it so badly? The lightsaber for the most part, was a Jedi weapon for the better part of its use. It highlighted a time in Anakin's life where he was fighting for the Light Side, against the Dark Side. Sure, he used it after Order 66 was placed, but that weapon was used primarily as a Jedi's weapon. After it moved ownership to Luke, it was also used to fight against the Empire, not for it.
Maybe he felt drawn to it as a reminder that he was a Skywalker, and that meant bringing balance to the Force. There is no reason I could see him wanting it so badly as a Sith. After defeating Finn (and not dealing an easy killing blow like he could have) Rey takes up Luke's lightsaber and fights against Kylo. Even with his training, Kylo did not deal any injuring blows to Rey. This could be because he is weak and injured, but I feel as if he had the skill to do so if he wanted. In the novelization, Kylo also exclaims, "It is you!" after Rey grabs he lightsaber with the Force. This seems to signify that he knows her from somewhere. Also, when finding out earlier in the movie that Finn and BB-8 were accompanied by a girl, he seemed to have an overreaction to the news. Did he know that there was an important person stranded on Jakku? That would lead me to believe so. While fighting at the edge of the cliff, Kylo had an obvious upper hand, but instead of pushing harder against her, Kylo tells her that he can show her the ways of the force. That she needs a "Teacher." The choice of words here is very important to me. He didn't say she needed a "Master." Wanting to be her teacher makes him sound more as if he wanted to share his knowledge and grow her into a more powerful jedi, not to just dominate her as a Sith master would his apprentice.
Maybe Kylo Ren wanted someone as powerful as Rey to join his fight, and to take down Snoke with him.
Now for the obvious questions:
Why would Kylo think that joining Snoke would help save the Galaxy? Kylo Ren if properly trained, and put into a position where he is close to the Supreme Leader, could very well betray him and throw the First Order into chaos. Thus saving the Galaxy and bringing balance back to the force, which is what I think he really meant by finishing what Vader started. To add on to that, what if it wasn't Kylo Ren's idea? What if Luke had masterminded the plan, and went into exile before it could be completed? If only he and Luke knew of the plan, it would be obvious that everyone else would still try to find Luke despite the exile. Why would Luke go into exile knowing that there was no plan in place to stop the First Order? Did he just plan on letting whole systems get wiped out because it just wasn't his problem anymore? I don't believe so. I think this was a carefully laid plan that required terrible things for a greater good.
All of that was a lot of reading, and I commend you if you read through it all.
Now for Rey, and why I think she is on the path to the Dark Side of the Force.
When we see Rey first, she is barely getting by on parts scrounged from scavenging trips. When she receives BB-8, she is offered way more food than she has every gotten for a scavenging trip. Instead of outright saying no, she had to consider giving up her new friend to someone who very well could have turned him into parts, over a bit of food. She ultimately says no, but we see that she has a selfish side that she almost gives into.
We see not soon after that she has an attack first, ask questions later attitude. When meeting Finn for the first time, she actually hits him hard enough to knock him to the ground with her staff. That's no way to confront someone who you really know nothing about.
Later, we see her firing the blaster Han gave her at stormtroopers. The look on her face is pure rage, as if she was so angry, that she was even possibly enjoying killing the stormtroopers. This scene is directly after finding out that Finn used to be one, so not only is she killing these troopers furiously, but she knows each one has had a life of their own, and they could even be decent people.
When being questioned by Kylo, he mentions how she wants to kill him. She doesn't deny it, and actually gives him her reason why she wants to kill him. All of this shows anger and hate, which is the path to the Dark Side.
Finally, during her lightsaber fight with Kylo, she is actively attacking him out of anger, and not for defense. Then, after hearing Maz's voice in her head to use the force, she doubles up and goes on full attack. This goes against what we know about a Jedi and the Force. Jedi are to use the Force for knowledge and defense. Never for attack. She very clearly goes on the offensive though, and strikes enough blows to permanently scar Kylo Ren. This is not the Jedi way, and this is the exact behavior we see from Luke on the Death Star that makes him stop and realize he was becoming what he was trying to defeat. Luke stopped his attack and threw down his lightsaber saying that he was a Jedi. Rey on the other hand fought until the planet itself separated her from her opponent.
It's not an end all be all theory, but this highlights the possibilities that Rey could end up turning to the Dark Side, while I believe Kylo is either a jedi, or is headed in the direction of one.
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