Former Hoofmaiden and personal servant to the previous Princess of the Crystal Empire, turned slave, and since freed through the efforts of Princess Cadance.
Once proud and loyal to her Princess, Citrine was broken by King Sombra, forced to perform terrible acts, and since returned. She does her best to perform her duties for Princess Cadance, forever grateful for her freedom, but is haunted by the terrible things she did.
A personal servant to the Princess, Citrine was consumed by the darkness of King Sombra's reign. He broke her will, making him a slave in mind and body, and used her to destroy his foes.
When the Justicar Bellerophon came to the Crystal Empire in search of Justice, his battle with Sombra had been carefully calculated. And while Sombra himself could not land a killing blow to the warrior, Citrine could. And at Sombra's command, she tearfully plunged a spear through Bellerophon.
Sombra's reign weighed heavily upon all the Crystal ponies, but Citrine alone dwelled with the blood on her hooves. As Celestia and Luna freed their Kingdom, she was consumed in the curse that swallowed the city, and vanished for a thousand years.
Since her ascendance, Princess Cadance has maintained Citrine as a Hoofmaiden, and many of the other Crystal ponies give her wide berth, sensitive to of her pain. She has taken great steps, but still held terrible guilt for what she did.
When Amethyst Vein and Shale Strata arrived in the Crystal Empire seeking Bellerophon's remains, they were introduced to Citrine. She told her story, and through her tears, took them to where Bellerophon died.
After the duo departed, Citrine returned to her duties. In part, the weight of her guilt had been lifted in telling the story, although she still has years of healing in the glow of the Crystal Heart before she ever stops fearing the shadow, and the stain it left upon her heart.