She is voiced by Inori Minase in the Japanese version of the anime, and by Brianna Knickerbocker in the English version of the anime.
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 left side of her hair, 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 tends to speak in a superficially polite manner and sometimes acts without thinking. She holds both respect to the point of worship and guilt toward her sister for an incident in the past.
Because of her respect and guilt toward her sister, she used to think of herself as inferior. After Subaru saves her, she falls deeply in love with him, becoming one of his most loyal followers. Rem will stick with him no matter what happens, even if Subaru rejects himself.
In her Oni Form state: Rem's personality drastically changes and becomes that of a mindless killing machine, murdering all without any form of hesitation and can even attack her own allies. Due to its violent nature, she only uses this ability with extreme caution.
Rem has lived with her parents and twin sister in an Oni village.
However, the village was attacked by the Witch Cult 10 years before the start of the series, her sister's horn being cut off by Faust.
The whole village got burned and destroyed, her parents and the citizens were killed, while her and sister were the only survivors.
Ever since, Rem devoloped a strong inferiority complex due to a sense of guilt for her sister's injury, so she made the upmost effort to become as ideal a servant as possible. But even having reached a certain level of perfection, she still has a low level of self-esteem and continues to idolize Ram.
Water Magic: Rem is skilled at Water Magic and Roswaal estimates her skill as being in the lower high. She is able to attack and heal using her magic.
Equipment: Rem wields a Morningstar in combat.
Oni Bloodline (鬼の血族 Oni no Ketsuzoku): As she is an Oni, Rem can enter her Oni Form, manifesting a single white horn on her forehead. The horn increases her physical abilities and acts as a gate which gathers mana from the atmosphere.
- Rem's birthday is on February 2.
- Rem's zodiac sign is Acquarious.
- Rem admits that is superior to her sister in household chores and cooking.
- In theory, Rem is also Ram's younger sister, since she was the second that came out of the maternal's womb.
- Shortly after birth, she and Ram were to be killed, because in their village the twins were considered a taboo because they were born with one horn instead of two horns.
- Rem is often considered one of the most popular character in the series
- She is also the first character to profess her feelings towards Subaru.
- As pointed out by Subaru, Rem's chest is bigger than Ram's.
- There is a special What-If story, in regards to her and Subaru running away, lived happily and even have two children; a son named Rigel, and a daughter named Spica.