In Re:ZERO -Starting Life in Another World- Season 4, Rem Will Wake Up As The Next Witch of Envy
This is the darkest Season 4 theory and it's blowing up right now.
Rem is still in her Gluttony-induced coma while her body is carried into the Auguria Dunes, one of the most miasma-dense places in the world. The Watchtower is built directly above what fans believe is Satella's shadow prison.
The theory claims: Gluttony didn't eat Rem's name and memories. He hid them in the Corridor of Memories to lure Subaru to the tower. Once Subaru unlocks the corridor, Rem's "empty" body becomes the perfect container for Satella, who has been obsessed with a silver-haired vessel for 400 years.
But Emilia is resisting Satella. Rem, with no self, can't resist. Fans point to Episode 9's miasma scene where an unseen woman gropes Subaru's heart. That wasn't Satella. The hands were too small. It was Rem, sleepwalking, drawn to Subaru by instinct while possessed.
If this pays off, the "Recapture Arc" won't be about saving Rem. It will be about having to kill her.