Hooooo boy. I sat down to write some thoughts of how I thought it could go and got hella carried away. Oops!
A lot of this is quite bad as I was trying to fit it around some of what we know. I also didn't go into any of the knew characters, really. It's absolute fan fiction crap, but isn't that what we're here for?
This post will use a couple of supposed spoilers that I read recently (though most of these are my own ideas), so avoid this post if you are avoiding spoilers.
At the beginning of the film, Rey, Finn, Poe, Leia and the still tiny Resistance are on the jungle planet. However, they are in the possession of a large-scale weapon which the Rebellion had been testing near the end of the war. The Fist Order somehow finds out about this and attacks, catching the Resistance off-guard. Rey, Finn, Poe, Chewie and the droids will escape in the Falcon while Leia says a tearful goodbye--she is staying behind to use the weapon, which will slow the first order from our Heroes' trail. She gives them one last gift of hope: inside the Rebel base they were hiding in in the Tantive III, the ship which holds 3PO's wiped memories. She tells them to find an old separatist base, where they may be able to find a droid army. Because 3PO interfaced with a battle droid years ago, his memories may have the code to reactivating an army.
Leia dies in the confrontation, massively crippling the First Order fleet. Ben feels this and is devastated and angry. Over the past year since TLJ he has remained fairly confident as leader, but this is where the recognizable cracks begin to seep back in. Many high officers begin questioning his leadership, and a rift begins to form. In an unstable mental state, Kylo hears a dark voice from beyond. (Alleged spoiler part) He seeks out a force-sensitive creature known as the Oracle in order to make sense of the voice, who tells him how to find this voice: Rey. Kylo is conflicted about this after the events of TLJ, but he needs to know more about the presence.
Rey and Co. head to Lando, who now owns a large droid business. They ask for his expertise in droids and such. He says he knows of an old Separatist base on a desert planet Pasaana, but it is in heavily First-Order controlled territory. Land helps smuggle the team onto Pasaana and waits for their pickup instructions once they've completed the mission.
Kylo and the Knights of Ren arrive on Pasaana, looking for Rey. Hey sends the knights and some FO troopers after Poe, Finn, etc. while he seeks out Rey. Rey senses him coming and we get the opening scene from the trailer. Kylo's TIE crashes and he confronts her in the desert. The light saber fight is at first normal, but (Potential Spoiler) their force-connection strengthens again during the fight, causing them to flash around various locations of the galaxy as they fight. Their battle is intense and emotionally-charged. Each has a moment where they could finish the other but they pull back. Finally, they end in a strange, watery location that seems like the Death Star ruins, yet in another world. Here they both here the voice/presence which haunted Kylo before. There they see Palpatine, who has preserved his essence in a sort of limbo. They accidentally 'release' him back into the universe, where he (Potential Spoiler) posses Matt Smith, a dark side acolyte. Palatine needs a being steeped in the dark side to attach himself to. Matt Smith's acolyte is just a temporary vessel: he wants Kylo as his new body.
Meanwhile, Finn, Poe, and 3PO head to the old base, which is heavily worn down and decaying. 3PO is able to interface with the system, but the battle droids are badly deteriorated and non-functional. However, 3PO discovers a droid factory from the end of the war on a mountainous, snowy planet where the resistance could build a new droid army. They get the coordinates and leave to find Rey. Rey and Kylo have gone their separate ways: Rey to the meet-up point and Kylo back to the FO. They are both, however, shaken by what they saw and both are clearly afraid. The gang reunites and exchanges the information they have learned.
Kylo returns to the First Order outpost on Pasaana, where the fleet has reconvened. However, it is not a warm welcome as he is met with a hostile takeover by Richard E Grant's character and the KOR/sithtroopers. The KOR have sensed the return of Palpatine, whom they are loyal to. They had been grooming Kylo to be a good host for Palpatine. They attempt to take Kylo prisoner but he struggles and escapes. He reaches out to Rey and finds her.
Kylo proposes a truce with the Resistance gang, who are understandably uneasy. However, knowing the threat of Palpatine they know they need him, and they enter an uneasy alliance. Kylo says he recognized the ruins from Endor, and that he needs to confront Palpatine there. The resistance, however, needs to go to the droid factory. They call Lando who comes to get them, but it's a fight to escape and they narrowly get past the FO. They hop on over to the droid factory, where they are able to build a small droid army, but time is running out and they need to get to Endor which prevents them from creating a large army.
The First Order has rallied at Endor under the command of REG and the KOR, where they know Kylo and Rey will come to. The Resistance arrives with the droid army and Rey and Kylo in tow. There they meet a group of local scavengers who scavenge the wreckage. Rey makes quick friends with them and they join the cause. The plan is for the Resistance to hold off the FO long enough for Kylo and Rey to beat Palps, after which they can then reinstate Kylo to the FO who then promises to stand down. Finn and Poe don't like this plan (they obviously don't trust Kylo), but Rey says its the only shot they have. Kylo and Rey head to the Death Star Ruins while the Resistance meets the FO head-on. Biggest battle in Star Wars yet. Space, air, ground, lightsabers, etc. Kylo and Rey put up a good fight against Palps, but they can't beat him. He reveals the truth: they, together, complete the force. They are the yin and yang, essentially. Kylo's bloodline was created of the darkness, and Rey was created from the light: while the Skywalkers were created by Sith experimentation into creating life, Rey was a reaction to this born of the light. That is why they together can open pathways. That's why Palps needed them together to escape. Together they are the beating heart of the Force.
Realizing this, they become in-tune and are finally able to overcome Palps and kill his host. However, this was always his plan. His essence then jumps into Kylo, who struggles to hold back Palps. He manages to hold him back for a while and tells Rey to kill him, but she can't bring herself to do it. Instead, she reaches out to him in the force and they are suddenly in a World Between Worlds looking place. Here, Anakin, Luke, and Han (and it's never made clear if it's really Han or just a vision) reach out to Ben and pull him to the light. We see spurts of his life: the good, the bad, his childhood, etc. Finally, Leia appears and embraces him, and we see a glimpse of her holding him as a child. She forgives him, and he is able to embrace the light and force Palpatine out. Palpatine is expelled and erased, and with him the Sith are gone forever.
During this, the Resistance seems to be losing at first, but the tide is turned when infighting begins in the FO. Hux leads an uprising against the new command, which gets him killed. However, this gives Finn the idea to appeal to the stormtroopers across the FO, inspiring them to stand against their oppressors. It's red storm troopers vs. white storm troopers, and eventually the resistance comes out on top. The Stormtroopers take control of the FO under Finn and stand down, ending the conflict. Rey knows Ben will not be forgiven easily, and helps him leave the planet on a small ship before returning to Resistance. She announces that Kylo Ren and the Sith are dead. Celebrations, yada yada.
We end on Ben now living in isolation on Tattooine, on the Lars homestead. It's a bit melancholy, but beautiful. He sits alone and watches the binary sunset, and for the first time in the trilogy, he smiles.
