Figure | Re: Zero Starting Life in Another World | Rem | Banpresto Espresto Stage Costumes

Rem is one of the twin maids who worked for Roswaal in the Re:Zero series. Rem and Ram are identical twins except for the color and parting of their hair. 

Rem has medium length sky blue hair that covers her right eye, large light blue eyes, and young features. She also has hair clips towards the left side of her hair, a flower-shaped ribbon on the same side of her hair, and a maid hairband. She looks nearly identical to her sister apart from her hair, eyes, and ribbon coloring. She usually wears a maid uniform, and since her chest is slightly larger than her sister's, she secretly changes the measurements to hide it.

Rem lived with her father, mother, and her elder sister Ram in an Oni village. Initially, because they were born with one horn each, it meant they were defective in the view of the Oni community, who believe in individual strength above all else, and were despised for it. They were to be killed as part of the custom of Oni to protect their pride as the strongest of the demi-humans. However, just before the execution, Ram displayed the potential of her power to protect them both, which shocked the community. Being allowed to live thanks to her older sister, who had an aptitude that had not been seen in a millennium among Oni kind, Rem spent the rest of her days in her shadow. Despite the presence of her sister also raising expectations for herself in the community, she could never meet them or surpass her sister in any area, which earned her disappointment from the other villagers. However, Rem loved her sister and accepted her place behind her and her parents still cared for them both deeply, even if she herself found it difficult to believe in front of the brilliance of her older sister. One night Rem's life changed forever when the village was attacked by the Witch Cult, during which her sister's horn was cut off by Faust. The whole village got destroyed and her parents and the other citizens were killed, except for her and Ram.

Ever since then, Rem's inferiority complex had deepened due to a sense of guilt for momentarily feeling joy for her sister's injury that night, so she made the utmost effort to become a replacement for her sister as ideal a servant as possible to atone for what she felt had robbed from Ram with her. But even having reached a certain level of perfection, she still has a low level of self-esteem and continues to idealize Ram.

(from Fandom Re:Zero Wiki)