Rey was the first to notice something was wrong. Being from the desert as she was she paid especially close attention to plants; every single one was new and fascinating. So when vines and thorns started growing in Finn's med bay room, she noticed. The plants started small, with a single thorny vine creeping up the wall behind Finn's head.
The vine was beautiful. It was a deep and welcoming green. Even its thorns were beautiful, a glistening purple that seemed to promise riches, power and water beyond compare.
Rey knew mirages. She knew how they acted on people and seeing the way Poe looked at the vine, half like it wasn't there, half like it was everything he had ever wanted, was all she needed to know. She reached for the vine. The thorns found no purchase against the calluses of her grip.
Finn's heart monitor went haywire and his chest rose several inches off the bed.
Rey dropped the vine. Finn dropped back onto the bed. His heartbeat dropped back to normal.
That was when Rey decided she needed to inform the General and the medical staff. The medical staff took the news seriously and had the entire base sweeped for similar contagion. Nothing. Whatever this was, only Finn was infected. Current theory was that he had brought it with him from Starkiller Base.
The General, on the other hand, paled. She marched straight to Finn's room and threw back the blanket over his chest. The vines had burrowed into his chest. Five black flowers the size of Rey's fist were growing over his heart.
The General took a step back. She composed herself and said, "On Alderaan, there had been a type of flowers that would entice sleep and produce good dreams. It was called the Mercy of the Valley. The Emperor had samples brought to Coruscant and from those samples Imperial science made --" the General gestured at the plant growing in Finn's chest "-- the Black Mercy."
Rey returns a Jedi.
They defeat the First Order.
The galaxy over, millions of Stormtroopers lay down their weapons and break free. They cite Finn as their inspiration.
After a first name, Finn finds himself being given a last name, Stormbreaker, to honour his role in making his people free. Because they are his people, the lost, the forgotten, the downtrodden. He takes care of them as best he can and flourishes.
He remains Poe's friend. They become best friends.
He marries Rey.
They have three children, one who is a daughter, one who is a son and one who is neither. They are all named after flowers. Poe is godfather to all of them.
One evening, General "Please call me Leia" Organa asks to speak to him privately. he leaves the kids with Rey and Poe and goes to talk to her.
She tells him they found his family. When he asks where, she says "Right here" and comes over to hug him.
Having learned what the vines were was not all that helpful if Rey couldn't figure out how to get rid of them. She threw herself into research. She would find a solution to this before it killed Finn. She had to.
The General provided Rey with as much information as she could, but she was a general, not a botanist. Rey would have to learn about Alderaanian plant life on her own.
So she did.
There had been considerable writing on the subject of the Mercy of the Valley, from the written-down oral legendary history to the scrupulously accurate botanical peer-reviewed articles, but most of the primary sources had been lost with Alderaan and there was nothing in what was left that said anything about the Black Mercy. The Mercy of the Valley's Blessing had dissipated in a day or two.
Rey found the Resistance's slicers and asked them for help in getting into the Empire's medical experiments.
"You don't want to see that," the short Zabrak slicer said.
"I do," Rey said.
"No, you don't," the slicer insisted. "There are pictures."
Rey noticed the steaming pot of caf and the mug that was still steaming but already half-empty and hadn't been washed in a long time. She put a comforting hand on the slicer's shoulder. "I know you mean well, but I really do need to see those files."
"If you say so." The slicer sighed and forwarded the files to Rey's datapad.
Rey began reading the files. There were indeed pictures. The slicer pushed the caf mug towards Rey in silence.
Rey left. She read the files all night. Well. She read the files until she ran out and spent the rest of the night in the brightest, most travelled part of the base, nursing a mug of Pantoran tsai mixed with caf.
There was no way to save someone from the Black Mercy. They had to help themselves, break free from the dream on their own.
It was, however, possible to tarnish the dream and turn it into a nightmare so the affected -- so Finn -- would want to wake up.
One day, in the middle of a pleasant sunny afternoon like so many other pleasant sunny afternoon, the sky darkens suddenly. It doesn't start raining, but the clouds hang heavy in the air, looking like rose petals about to cry. But they never to cry and the rain never does fall and the sun never comes back.
Finn's son dies first. It's an accident, everybody says, but that doesn't stop Fin from feeling guilty or Rey from growing distant. She grows harsh too, and bitter.
When their other two children die, Rey leaves. Poe leaves with her and Finn finds himself alone and betrayed.
Finn is alone. Even the General -- even after all these years, he is still hard-pressed to think of her as his mother -- distances herself from him.
He makes a series of unfortunate decisions.
It is when the General compares him to her father, to Darth Vader, that he realises something is wrong. She has never referred to him as her father before -- and besides, wouldn't a comparison to her other son make more sense?
Now that he has seen one crack in the facade, the rest soon begins crumbling as well.
The voices of several people of the Resistance -- the General foremost among them -- seem to be coming from faraway or sound as if the speaker is under water. And the clouds still have not left. They retain their odd, flower petal like pattern.
Much like the Force, that's not how weather works. That's not how anything works.
The sky cracks open, like a skull splitting apart as it falls onto duracrete.
It feels a little like being born and a little like the rain finally coming after too long-lasting clouds, but mostly it feels a lot like pain.
And Finn wakes up.
Finn woke up gasping and clutching at his chest. The med team rushed in, practically tearing his hands out of Poe and the General's grasp. They took more care to remove Rey's hand from where they were tangled from the vines around his head. They needn't have bothered. The Black Mercy had been falling to ash almost before Finn had woken up.
"He'll be fine," the General said. Through her newly acquired Force-senses, Rey could tell she both believed this and had been rattled really badly by what she'd had to say to break Finn out of his Black Mercy dream. The General had a core of steel and starlight and continued, "If he still wants to be my son once this is over, I would be honoured."
"You should tell him that," Poe said. He got up and offered his hand to the General. "Let's get him caf for when he wakes up."
"No psychoactive substances!" one of the med team shouted at their retreating backs.
Rey remained seated. Her legs felt as uncertain as shifting sands and would not support her weight. It was not just her use of the Force, it was worry for Finn. He'd loved her, in his dream. She loved him even outside of the dream -- did he?
They'd had children, three unreal children that felt real to her and even realer to him and that they would have to mourn, together.
If he remembered. It was possible he wouldn't. She hoped he didn't, he didn't deserve that pain. Neither did she, but she would gladly take it on to save him.
"You can go see him now," the same member of the med team told Rey. Rey was on her feet before they were done talking. Her legs were wobbly, but they carried her where she needed to be.
"Hey," she told Finn.
"Hey," he replied.
"I missed you," she said. Then, in a rush, before she could back out, "Can I kiss you?"
His smile was all the answer she needed. So she kissed him.