This post has been updated according to the events portrayed in Season 2 of Re:Zero.
When Emilia-tan asks “Who is Rem?” in the carriage, it literally sends a chill down Subaru’s spine. Just as he thought that he’ll be having a good time, Subaru was again thrown in despair. As Re:Zero Season 2 premiered, the major cliffhanger surrounding Rem and why Emilia seemingly had no memory of her were addressed.
We know that Rem helped Subaru, Lady Crusch and her knights take down the White Wale and gets injured in the process. Subaru sends her away to the capital with Crusch so that she could tend to her wounds and get some rest. Rem, though disheartened, agrees with Subaru and leaves. After this, Subaru goes on the defeat the Sin Archbishop of Sloth Petelgeuse Romanee-Conti and further protect Emilia from the Red Stone’s explosion.
What has happened to Rem?
To answer the question quickly,
While Rem was returning to the capital along with Crusch and others, they were attacked by the Sin Archbishop of Greed, Regulus Corneas and Sin Archbishop of Gluttony, Ley Batenkaitos. The Witch’s cult wanted to challenge the people who took down their pet, the White Whale, and hence massacred their party.
The the sin archbishops were easily able to overpower Rem and Crusch. However, she is not dead. Rem is suspended in a coma like state after her fight with the sin archbishops. She even used her demon form to attack Gluttony, but she is eventually defeated.
Everyone other than Subaru has forgotten who Rem is.
Why did everyone forget about Rem?
The reason why no one remembers Rem is because of Ley’s Authority of Gluttony. This authority enables him to eat the memories and name of his opponent.
When he eats someone’s name, their existence is erased from the minds of everyone, destroying any human relationships along with negating any contracts with Spirits. When someone’s memories are eaten by Ley, they become amnesic (like Crusch).
Rem has both her name and her memories eaten by the Sin Archbishop of Gluttony Ley Batenkaitos, which makes Emilia and everyone other than Subaru forget her. Even Ram won’t have any memory about Rem, which is somewhat similar to the effects of the White Whale’s fog.
Can Subaru save Rem this time?
Everytime Subaru progressed in the plot, his revival points or checkpoints moved ahead. After, finding out that Rem was in a coma like state, Subaru kills himself in order to save her, but finds that his save point has been updated to his interactions with Emilia in the carriage. This event takes place after Rem is attacked by the Sin Archbishops of Greed and Gluttony, which makes it impossible for him to save her using Return by Death.
However, Subaru has not given up. Just like Rem passionately stated to the archbishops, he has vowed to get her back, come what may. Still, at this point, it is very difficult to judge and point out how Subaru could save Rem. But then, we sincerely hope that he does and our beloved Rem comes back to us soon.