The Scarlet Guard were the military force that served the Scarlet Empress and enforced her will across Hyspero. The Eighth Doctor thought that they were a "terrible lot". (PROSE: The Scarlet Empress) They used daggers in combat. (PROSE: Wildthyme Beyond!)

Every member of the Scarlet Guard had unique and elaborate tattoos on every inch of their skin which depicted Hysperon flora and fauna. The tattoos used green and blue ink. The tradition of tattooing the guard began during the reign of Empress Cassandra. Guards has to remain bald to display the tattoos on the top of their heads. In the public, the Scarlet Guard covered themselves with crimson cloaks. In order to let the Empress fully appreciate the tattoos, the guards had to remain nude while in the Scarlet Palace. By the time of the Abbasid Era, generations of Scarlet Empresses had amassed a gallery of the hides and severed heads of deceased members of the Scarlet Guard. (PROSE: The Scarlet Empress)

While the Scarlet Guard were a force that was feared by most of Hyspero, (PROSE: The Scarlet Empress, Wildthyme Beyond!) they were encouraged to flee before allowing any part of their skin to be damaged in combat. Miniature T-Mat units on their belts allowed them to escape at a moment's notice.

The Eighth Doctor, Sam Jones, and Iris Wildthyme were pursued by the Scarlet Guard during their quest to reunite the Four and usurp the Scarlet Empress. During their adventure, the trio encountered the Scarlet Guard in Hyspero City, a restaurant owned by a Steigertrude, the Forest of Kestheven, and in a region of Hyspero covered with snow and ice. After the Scarlet Empress was overthrown, the gallery of the hides and heads of deceased members of the Scarlet Guard was dismantled and its contents were buried in the desert. (PROSE: The Scarlet Empress)

The Scarlet Guard patrolled Hyspero for Iris Wildthyme after she came to Hyspero with a few of her friends to prevent Anthony Marvelle from opening the Ringpull. The Scarlet Guard found the Celestial Omnibus while Iris was away and took Simon, Barbra, and Jenny Winterleaf to the Scarlet Empress.

The book Iris Wildthyme Returns to Hyspero featured a battle between the Scarlet Guard and refugees from the Obverse. (PROSE: Wildthyme Beyond!)