He had his marching orders from Palpatine- kill her. Kill the Jedi. Kill the one person that he could never deny his connection to. As if he wasn't struggling with his spiral into the light as it was. Perhaps if Snoke had not insisted he kill her things would have gone differently in the throne room all those months ago.
Did these decrepit, old tyrants not realize they were asking the one thing that would spell their own demise at the hands of Kylo Ren? She was not to be harmed, she belonged to him.
She originated in the dark- meant to be the dark empress that would destroy the galaxy. He smirks at the irony of it. He is born of the light, a prince of light if you will…. And yet he chose to side with the Dark. The Supreme Leader and the Scavenger have a similar origin story. They have both exchanged one side of the Force for the other throughout their lives.
He would not kill her. He would pursue her, understand their strange bond, and draw her close to him to keep her safe. Light side, dark side…. Their side. Ren doesn't realize the shift from light vs dark in his own mind. Everything is gray. Everything is about her and her survival. This bond must continue for the sake of his sanity.
Rey, though born to the dark side, has found her place in the light- becoming the warrior princess of the resistance under General Organa. From darkness, she rose and found her belonging among friends and created a family.
He fell from the light, from his distinguished family, and embraced the power of the dark side to chase away his loneliness and keep his distance from those that should have been there during the struggles of Ben Solo but weren't. Thus, Kylo Ren came into existence. Kylo needed no one and nothing- simply strove to be the most feared member of the Sith . So, Ben retreated behind the mental walls erected during years of torture and training with the Sith, to sleep and hide from the world that was so cruel.
It's no wonder he struggles with his orders. Ben Solo has never wanted to resurface from his long slumber until this girl became a target to the First Order. Ben has heard the call to the Light, and he is breaking through the walls of Kylo Ren. Wrestling with his alter ego to save this scavenger girl, this dark empress turned warrior for the light. She has been in his mind and seen his loneliness- and reaches out for him to join her side and be with her.
He sees her pain in the dessert on Pasanna- he feels through their bond that she is more heartbroken to lose the Wookie than she felt at the passing of Luke. He fights with himself- wanting to show her that the Wookie was not harmed, that he lives, and Ben will keep him as safe as he can on his own ship until the Resistance can mount a rescue attempt. After all, Ben knows Chewie is capable of surviving capture- how many stories had he heard as a young boy of the daring adventures of his father and the Wookie?
He WANTS to tell her this. Kylo Ren is in control, though- and will not show weakness while the Knights linger in the atmosphere. Their Force abilities are limited, but not nonexistent. A plan will come to him, if the Resistance doesn't beat him to it. Ben was a resourceful child… and with the cunning of Kylo Ren, there is no doubt that he will give Chewie back to her.
Having Chewie in residence on his Star Destroyer is a bit more complicated than Kylo would have liked- he feels the attention and scrutiny of that weasel, Armitage Hux, whenever the Wookie is mentioned in reports and debriefs. "What is to be done with him? When will we execute the beast, Supreme Leader? No information is forthcoming from the Wookie, why not kill him and move on?".
Kylo is exasperated when he's finally alone in his chambers. He stopped to see Chewie, but he had to keep a necessary distance… an emotional front up with his Uncle Chewie. He could feel Chewie's mistrust and hurt towards Kylo Ren, and it took every ounce of willpower -curated after years of Snoke's torments- to keep Kylo Ren's mask in place and hide Ben Solo away. Chewie would know- Chewie always knew Ben's moods and feelings.
A beep on his communicator alerts him a message is incoming from the Bridge. He debates ignoring it and letting the millions of soldiers run themselves for a couple hours while he rests. He can't remember the last time he slept more than an hour…
It's Vicrul- reporting in. His scavenger has been spotted in Kajimi. Showtime.
He orders Chewie to be moved to an empty prisoner block- under some pretense about isolating the prisoner to encourage him to talk- and takes his knights with him to search for Rey on Kajimi.
Without acting too suspicious, he is removing the most dangerous members of the First Order to clear the way for Rey and her band of misfits. He doesn't know who she has with her on her adventures in Kajimi- but he will give them whatever time he can to formulate a rescue plan and act on it while he keeps his destroyer nearby.
He spots a small craft take off as he lands his whisper TIE- knows it's her, feels her resolve and hope for Chewie. It satisfies an ache in his chest that began in the Pasanna desert. Maybe he will sleep a little better tonight.
He stays on high alert, expecting a call from the main bridge alerting him and his knights that they've been infiltrated… he is on edge in his mind, worrying that Rey won't slip past the hordes of troopers that roam the halls in batches… but he has done what he can for now. He turns his attention to terrorizing the people of Kajimi, keeping his knights focused on their immediate surroundings and using their laughable Force ability to search for Rey here on the ground, where he knows she will not be found.
He feels their connection brewing after a few sweeps around the main town, feels her eyes on him and her surprise and concern at seeing him. He wonders why she feels surprised…after all, this connection between them flares to life at the most unusual of times.
He keeps his mask on, keeps his feelings locked away with his knights at his back. Ben wants to reach out, ask if she found Chewie, and tell her to hurry and get out of this galaxy while she can. Kylo stands firm, shuts Ben out, and focuses on Rey and their conversation- before he realizes what's happening, he's whipping his lightsaber around and engaging her in a test of strength.
He senses how much she enjoys trading a few blows with the saber, Kylo Ren understands the importance of getting in a few practice rounds with her so she will build her skills up. No one in their rag tag resistance could offer her a real challenge. Kylo is proud of how far she has progressed, knows that she has worked hard on her fighting styles. He longs to correct her, teach her more, and spend time discussing the merits of the various fighting style. But there is no time. He must ensure she has what she came for- the Wookie and the spear- and avoid suspicion from the First Order hounds that nip at his heels.
At last he can deny it no longer, he senses the Wookie's movement on his destroyer- a small force signature accompanying Chewie wherever he is going which surprises Kylo Ren. It cannot be Rey. She is in front of him, trading swings with the Skywalker saber. The knights pick up on something- they sense Rey above them, and Kylo realizes its time to go, time to return to the ship and confront her dramatically in keeping with his style.
He gives the command, lock down the ship. He knows the knights hate being treated as though they are a platoon of troopers- mindless and unremarkable. Their pride in their work gets in their way of being efficient many times. Giving them the order to lock down the ship means there will be a minor delay while argue amongst themselves who will follow the order and contact the security force on the Bridge.
Kylo and Ben have bought Rey as much time as possible- now he needs to get back, engage with her and see that she survives another encounter with the First Order.