Ruby is a slight, dark-skinned half-elf teenager with long red hair, including one narrow braid threaded with emerald beads. Her eyes are vivid green, and her pointed ears are partly hidden beneath her hair. She wears black pants with red panels, orange flame-patterned boots, a red shirt, a yellow vest decorated with red jewels, brown gloves, and a flowing red cloak. A satchel crosses her body and holds a pack of darts. A dagger hangs at her hip, while a black dragon-headed staff with a ruby set between its jaws rests across her shoulder. Her Emeraldheart family ring hangs around her neck on a chain. A baby red female dragon named Fire often perches on her shoulder. Ruby moves with restless, deliberate confidence, constantly shifting her weight as though ready to run or strike, and she has a habit of standing just a little too close when she wants someone unsettled.

Ruby is clever, suspicious, theatrical, and fiercely possessive of the few people she considers hers. She can be charming when she needs something, but her charm often has a sharp edge. She enjoys making arrogant people look foolish and has little patience for rules that protect the powerful. Beneath her confidence is a frightened child who still expects to be abandoned, so she tries to control every conversation before anyone else can control her.

Ruby Emeraldheart was four years old when her family carriage was attacked on a lonely road. In the confusion, she fled into the woods and reached the nearest town alone. She could not prove that she was the eldest child of the Noble Emeraldheart family, and the officials who found her sent her to the local orphanage. Ruby remembered only fragments of her former life, including the weight of her family ring and the smell of smoke from the ruined carriage. Years later, she still does not know whether her parents and siblings survived, or whether the attack was meant to erase the Emeraldheart line entirely. At the orphanage, Ruby met Nova Lightsong, a nine-year-old girl with a feathered cap and a battered lute. The two became inseparable, eventually treating one another as sisters. Around that time, Ruby's fire magic began appearing in sudden bursts, first as sparks in her palms and later as uncontrolled flames when she felt frightened or angry. Ruby and Nova eventually escaped the orphanage and traveled together, using Nova's music and Ruby's budding sorcery to charm, deceive, and swindle travelers. During their wandering, they discovered a baby red dragon. Ruby named her Fire and claimed the hatchling as her companion. Ruby now seeks the source of her strange magic, the truth behind the carriage attack, and any surviving members of the Emeraldheart family. She is willing to manipulate, threaten, or betray nearly anyone who stands between her and those answers.