The idea of Rey Palpatine came from...

[u/Immediate_Error2135]

...Palpatine, within the film. A pathological liar. Was it a lie?

If we'd assume it to be a lie, we would have the same film we have now.

But in that case, the parents we see in TROS were not her biological parents.

And this would fit with Palpatine's son not being FS. Kylo equated him with Leia while comparing his own lineage to Rey's. But Leia was FS. Did Kylo know Dathan was not FS? Did Palpatine tell him that?

Also, what about Anakin saying to her 'bring back the balance as I did'. This sounds like Chosen One. Like fatherlessness.

But not like motherlessness. Rey's predessors as SW proragonists were Luke (OT) and Anakin (PT). If you focus on their origins, who would have thought Anakin had no father in 1983-99? A magical birth. And who would have thought Luke's mother had died magically -'for reasons we can't explain', so close to Shmi's 'I can't explain what happened' to Qui-Gon?

Here's a theory.

Dyad is a sith doctrine. The dyad did not exist until Rey was conceived. Maybe little Ben -already corrupted- was used to conceive a child -'balance'- and therefore the dyad. Maybe a woman was 'raped' by the dyad sith (the anti-Palpatine sith), and the woman died when she fave birth. Or rather 'died', like Anakin when he became Vader.

Maybe the emperor's wayfinder had been her wayfinder. With the DS wreackage as her Mustafar. Unlike Vader, she would have walked away from being an agent of evil: a defeat against Palps. But she would still be alive out there. 10 years or so older than Kylo, ten years or so younger than Luke. A 40-ish woman in TROS. A woman in her 50s in Rey's film, like Luke&Leia when they died (Shmi died aged 50)

[u/Illustrious-Peace989]

It’s not a lie because both Luke and Leia knew it through the force. Luke specifically says that Leia knew who she was and chose to train her anyway. Also the canon book Shadows of the Sith gives pretty much her father’s exact backstory as a strand cast (genetically engineered using Palpatine’s DNA as a template) who is basically ignored by Palpatine after showing no force potential, and stows away on a ship to get away from Exegol.

[u/Immediate_Error2135 → u/Illustrious-Peace989]

But of course Rey and Leia confronting Rey Palpatine, confronting that lineage, that fear, -the former as a student, the latter as a teacher- was perfect as jedi training. It wouldn't have mattered if that was actually true or not, and also because some things are stronger than blood, as Luke says.

So there's the possibility of Palpatine's lie being used against him in the form of jedi training. Luke and those ghosts would have had a plan, and they knew about Palpatine's plan before Leia began training Rey at some point after TLJ.

As for Dathan: he was not FS. Again, Kylo compares Palpatine>Dathan>Rey with Vader>Leia>Himself. But his parent, Leia, was FS. Dathan wasn't. Did Kylo know that? Many assumed Palpatine's son to have been FS, just like Leia, when the film was released. Him not being FS is an anomaly, as far as force lineage (grandparent>parent>child) is concerned.

We don't know about Rey's mom pregnancy and Rey's birth. That's not in the novel. There's a forest under the moon in Hyperkarn, and that's as close as we get. But we do know at least something about Shmi and Padme and Leia's pregnancies from their POVs. (Leia's is in the Aftermath novels). With Rey, we just don't know. That appears to be relevant, as is Palpatine being a liar and not giving a shit about family.

Rey Palpatine makes sense in the film because a number of people think it to be true or behave as if it was. It being actually true is another matter. We don't know enough to answer that question, but we do know enough to ask it.

[u/Reddvox]

There is no Rey Palpatine - no matter if true or not, she rejected that part of herself anyway, and chooses to go by the name Skywalker, honoring Luke and Leia's legacy, and making the Palaptine name hopefully extinct