Dr. Rebecca Holiday is Providence's chief research officer, a position she earned due to her expertise in nanite-technology. Along with Agent Six, she is responsible for taking care of Providence's secret weapon, Rex. She takes her job very seriously, constantly monitoring Rex to ensure his safety to the point of acting as a surrogate mother.

Rebecca Holiday is a tall woman with light green eyes and dark brown hair that is neatly kept in a bun. She wears a white lab coat with an orange shirt underneath, a gray skirt and black high heel boots.

Doctor Holiday has also performed many complex tasks and tests involving nanites, such as attempting to disable them. Her intelligence allows her to quickly piece together facts and figure out solutions to problems with ease. With Holiday's logic and guidance, Providence has completed various missions and survived life-threatening events, such as the Lomitle invasion.

There was a time when Rex had been attacked by a venomous Chupacabra and needed a cure right away. Holiday was sent a blood sample of the creature and synthesized an anti-toxin. There was also a situation where Holiday's EVO sister, Beverly, was mutated by a machine Branden Moses had created. Using her knowledge and the information he gave her, she reprogrammed his machine to break apart nanite particles, ultimately making her first cure.

Sometime in Doctor Holiday's life, her younger sister, Beverly, went EVO, having an intense effect on her. It is implied that Holiday joined Providence in exchange for the guarantee of her sister's safety, who was an incurable EVO Ever since then, she requested that Providence keep Beverly stationed in The Hole for treatment.

In the early days of Providence, Holiday served as a medical assistant to Doctor Fell. However, she was greatly opposed to Providence's protocol for handling EVOs, which was to contain or destroy them. Although she had no authority in the matter, she believed there was another alternative—finding a cure.

One day, Six discovered Rex, who had the ability to cure EVOs. Six presented Rex to Holiday, who was overjoyed with the discovery, but promised with Six to not tell White Knight, who was crazed with killing EVOs. Later, White Knight was mysteriously able to get her to confess, and locked her in a cage to prevent being stopped. Dr. Fell was later fired by Providence following his attempt to dissect Rex and was soon replaced with Dr. Holiday.

Despite being a researcher, Doctor Holiday has been trained by Providence to defend herself. Holiday possesses quick reflexes, as seen when she effortlessly dodged three EVOs that Breach teleported into a Providence containment room. Additionally, Holiday is proficient with the use of firearms. In particular, she has used Providence machine guns and missile launchers to defend her allies from EVO piranha that attacked their boat while on their way through the Amazon River. When Six and Rex were about to be attacked by a massive EVO in Abysus, she quickly jumped in front and fired her pistol at it until it slowly retreated. Although Holiday is generally able to take care of herself, there have been multiple times where her low accuracy with firearms and her low strength level have almost gotten her injured. Only once has Holiday ever demonstrated her agile ability to do tumbles and back-handsprings to dodge Caesar's machine.

With her hand-to-hand combat skills, Holiday has managed to take down her enemies on some occasions. Once, while being restrained by one of Branden Moses' men, she easily fought him off and grabbed his gun after it had been knocked out of his hand. For a woman her size and physique, Holiday is able to punch hard enough to throw males, slightly larger than her, back with her blows.

After a six month gap and Rex's disappearance, Holiday cut ties with Providence and went on a mission with Six to find Rex. Finding him, they teamed back up and fought against the orders of New Providence and Black Knight. She later regained her position as Providence's chief researcher. After the six month gap she became considerably more aggressive and stern, as she threatened people more often and was much more trigger-happy with her weapons.

Noah guessed her age at 28 and she is a fast runner and capable of running in heels and has three PHD's and is also a lousy cook, as the cake she made for Rex's birthday was as hard as stone

Dr. Holiday is also very proficient with an EVO blaster, Grappling hook, Providence pistol and a Machete