Rem is one of the twin demons who work at Roswaal's mansion as maids, Rem is Ram's younger sister. She has blue hair which she wears parted on the left, and still has a full horn, which grants her magical power. She does work at the mansion, although her ability to cook is better than her sister. She used to have an inferiority complex towards her sister.

Bearing an intense hatred for the Witch's Cult, Rem initially accused Subaru for having the Witch's scent, that resulted in her killing him twice. After Subaru saves her from the mabeasts of Elior Forest, becoming her "hero", Rem discards her suspicions and falls deeply in love with him, and even when he turns her down in favor of Emilia, she still becomes one of his most loyal followers. An extra story in Arc 3 of the novel tells a "What If" story about what could've happened if Subaru and Rem had decided to run away instead; they lived happily ever after with two children.