One of the biggest questions in Star Wars: The Force Awakens surrounds the family history of Rey, the young junk scavenger on Jakku who later learns the way of the Force to help find Luke Skywalker. While many fans believe she is part of the Skywalker or Kenobi family trees, there’s one theory out there that suggests Rey comes from the Dark Side of the Force and is, in fact, Emperor Palpatine's granddaughter.
The theory originated with writer J. Kenji López-Alt on Medium, but was later expanded upon by Vincent Vendetta on YouTube. The theory boils down to how Rey is presented in The Force Awakens: Her lightsaber fighting style is reminiscent of Emperor Palpatine's in Revenge of the Sith, in that they both use a thrust-forward attack style that no other Jedi Knight or Sith Lord uses throughout the Star Wars saga.
Palpatine's voice can be heard during Rey’s dream sequence at Maz Kanata’s castle as well as during her lightsaber battle with Kylo Ren in the screenplay and the novelization, which are both considered canon. In addition, both Emperor Palpatine and Rey have English accents. This implies a connection to the Dark Side as, in the Star Wars universe, most of the characters with British accents are villains (Obi-Wan Kenobi and Mon Mothma are two of the few exceptions). Furthermore, Daisy Ridley and John Boyega are both British, but for The Force Awakens, Boyega speaks with an American accent while Ridley uses her natural accent.
The theory further suggests that Rey has a lot of anger inside of her, which comes out as rage when she’s shooting at Stormtroopers with her blaster, when she derives pleasure from reading Kylo Ren’s thoughts and fears, and during her lightsaber battle at the end of The Force Awakens. If Rey doesn’t learn to control her anger and rage throughout the sequel trilogy, the theory posits, she may very well end up on the Dark Side of the Force.