SPOILERS for the entire series of Re:ZERO
Subaru is the most polarising figure in Re:ZERO. He is the reason some people were drawn to the show, and the reason others refused to watch past a certain point. The only other character who has similar control over the audience is Rem, the blue-haired maid voted best girl by half the internet around the mid-point of Re:ZERO.
As a feminist viewer and big fan of the Re:ZERO anime, Rem is a problematic character for me. On the one hand, I like her. I wouldn't expect to like a subservient maid character, but something about her deadpan smackdowns and thinly veiled distaste for Subaru won me over early on, while her loyalty, fierceness and vulnerability made her an endearing, stand-out character. I completely understand her popularity. (Respect to the Re:ZERO production team - that is quite the accomplishment.)
On the other hand, she’s a self-loathing young woman in a sexualised maid’s costume who spends the entire series devoting her life to the people around her. Rem is a strong and beautiful woman who hates herself and falls in love with an otaku, and anime fandom adores her for it. That’s uncomfortable to see, especially when most of the love came after the deadpan and distaste had been dropped in favour of rose-tinted love goggles for our polarising protagonist. It's a wish fulfilment step too far in an otherwise sophisticated story of complicated characters.
However, it becomes easier to watch if you stop thinking of Rem as a character in her own right. If Rem is not supposed to be a fully realised character, with motivations and ambitions independent of the people around her, then suddenly her character makes sense. If Rem's primary purpose in Re:ZERO is to be a foil to other characters, we can’t resent her lack of identity away from Ram or Subaru or mourn her loss when she inevitably disappears from the narrative (though we can of course criticise both). By then she will have served her purpose and have no further reason to exist.