In the prequels, it was fear, anger, jealousy, and lust for power
that put Anakin Skywalker at risk of turning to the darkside. His character traits are what defined his arc not the superficial elements like heritage or innate power.
While Rey being a vergence in the force is an interesting idea, I don’t think her having a god-like midichlorian count justifies her inner conflict with the darkness or substantiates an arc that consists of accepting one’s darkness.
I think the idea with the most potential in this case is Rey discovering that she killed her parents, highlighting her anger as her forefront character flaw. This places the two sides of the coin (Rey and Kylo) on an even footing, reflecting the dyad and giving the audiance a legitimate fear that she is indeed at risk of turning.
-“I pushed you in the desert because I needed to see it, I needed you to see it, What you did to your parents,so long ago”.
-"They sold you because they feared you. Search your memories. See them. It was you that destroyed the ship. You killed your parents Rey. We are more alike than you think.
There’s also an opportunity to tie in to the force awakens Kylo presumably knowing of a girl in the desert, “what girl?”, which could play into the dyad.
In the hangar, Kylo could tell Rey that Palpatine had been grooming them all this time, that he sensed their darkness since they were children, declaring that Kylo and Rey are a Dyad, and that they will inherit the dark throne.
“It was Palpatine all this time. He sensed my power, as he sensed yours. As a boy I had visions of a desert, a girl lost in the sand, alone. It was you, Rey. We are a dyad in the force, Two that are one. We will kill him, and take the throne.”
