Rum is the living doll assigned as the face for Shirley. She is very timid and barely speaks, afraid to upset others; eventually, Emilico's contagious joy helps bring Rum out of her shell a bit. Rum has a weaker bond with her shadow master than other pairs.

She has an imaginary friend named Rummy, focused in her left index finger and represented by a black ribbon(Shirley has a matching white ribbon). She crooks her finger slightly when "talking to" Rummy.

During the Debut arc, Rum is revealed to have very good photographic memory.