Rem operates as a maid under Margrave Roswaal L Mathers alongside her sister Ram in the Re:Zero universe. Her appearance features sky-blue strands obscuring her right eye, light-blue irises, and a modified maid uniform subtly accommodating her fuller figure compared to Ram. Initially distrusting Subaru Natsuki due to detecting the "Witch’s scent" on him, her stance shifts to profound devotion after he rescues her from a horn-induced rampage—a power she later masters, steeled by devotion to him.

Her past harbors tragedy: the Witch Cult’s annihilation of her village, her sister’s severed horn, and lingering self-doubt from perceived inadequacy. Following Lye Batenkaitos’s consumption of her name and memories in Arc 3, she enters suspended animation until Arc 6, awakening amnesiac alongside Subaru and Rui Arneb in the Sacred Vollachia Empire. Crossovers preserve this memory loss while retaining her disciplined prioritization of duty, fierce loyalty to Subaru, and protective tendencies that escalate to violence against perceived threats.

Within Isekai Quartet, she serves as a school nurse alongside Shalltear Bloodfallen, employing pragmatic methods like her flail’s chain to immobilize disruptive patients during examinations. She supports Subaru in events like talent shows, balancing encouragement with clashes over trivialities like condiment choices, reflecting tensions between her allegiance to him and her sister.

In *Another World*, she joins a strategic retreat from golem swarms, reuniting with allies at a village regrouping point. Her contributions focus on collaborative efforts to dismantle the golem threat and return home, aligning with her steadfast identity as a guardian bound by responsibility. Interactions with figures like Albedo reveal mutual respect regarding devotion, while exchanges with Shalltear hint at understated insecurities tied to physique.