She is voiced by Houko Kuwashima in the Japanese version of the anime and Trina Nishimura in the English version.
Rebecca has short, neck-length dark hair that lies down in spiky tufts, with tufts at the back spiked upwards. Another short tuft stands straight up in the middle of her hair. She has brown irises and a fair complexion.
Rebecca usually wears a white shirt underneath a brown leather jacket with green pants and black suspenders. The shirt is a collared short-sleeve that flaps down to her waist, separating at the middle to expose Rebecca's navel. The leather jacket is also short-sleeved and has yellow fur around the end of the sleeves and the collar. Her pants come down to her shins and she wears brown travellers' shoes. Underneath her shirt, Rebecca wears a black undershirt or singlet. Balar takes the form of a golden bracelet on her right hand.
Rebecca has a very upbeat personality and tomboyish style of behaviour. She is playful, often making jokes, and is eager to participate in battles. She is quite violent and has a destructive nature, rivalling that of Khamsin, perhaps even surpassing, as she has no qualms with using her abilities for mundane tasks, such as blasting through doors instead of simply opening them. This kind of behaviour has given Rebecca a reputation, warranting several nicknames such as "Bomb Woman" by Shana, "Stupid Bomb" by Flieder, "Incorrigible Child" by Sophie, "Son of a gun" by Samuel, and "Bomber" by members of Bal Masqué.
Despite her independent and unruly behavior, she values friendship and strives to honor her words, as she chose to help Wilhelmina in her quest to save Shana to return the favor owed centuries ago instead of staying back at the Outlaw branch in Tokyo to help coordinate the war.