Miriael Sabathiel is a former Sister-Superior of the Adepta Sororitas' Order of Our Martyred Lady who is the only known Battle-Sister in the history of the Imperium of Man to have willingly turned to the service of Chaos, in this case becoming a Chaos Champion of Slaanesh, the Dark Prince.
A sign of strength for the Adepta Sororitas is the fact that in their entire history only a single Sister, Sister-Superior Miriael Sabathiel of the Order of Our Martyred Lady, has willingly fallen to the power of Chaos. The exact circumstances of her fall to the corrupting influence of the Dark Prince is unknown; however, what is known is that Miriael eventually turned from the Emperor's light to the worship of Slaanesh, and now serves as one of the Prince of Pleasure's greatest Chaos Champions. Miriael wanders the galaxy since her betrayal of the Emperor's cause, slaughtering the enemies of her God.
A full Mission of Sisters of Battle from the Order of the Argent Shroud vowed on Ophelia VII to capture Miriael. All of them swore themselves to Slaanesh after being overwhelmed by the unholy will of Sabathiel. These fallen Sisters now form her retinue. Canoness Olga Karamanz of the Order of Our Martyred Lady tried to apprehend Miriael upon the world of Cauldrus Prime, proclaiming a desire to help her find redemption, but was murdered by Miriael for her troubles. Inquisitor Tosak set out to hunt her down in the Sactifiza System. He was tortured to death in the bowels of a shattered hive city, bereft of his faith.
An entire Shrine World fell to Slaanesh through the machinations of Miriael Sabathiel. It will not be long before Miriael's warband of fallen Battle-Sisters and other, less elite Renegades is large enough to challenge the most powerful Slaaneshi warbands, those led by former Astartes of the Emperor's Children Traitor Legion. The cold fervour that Miriael applied to her life in the Adepta Sororitas is now applied to her worship of Slaanesh. Miriael dreams of the day she can lead a cruel mockery of an Imperial Crusade, and sacrifice all those who do not serve the Dark Prince.
- Armour of Ecstasy - Miriael's Sororitas Power Armour has been warped and corrupted by the will of Slaanesh. It has been repainted and is now decorated with the blasphemous iconography of Chaos and Slaanesh in particular. Her body is sealed into this armour as one of the mutational "gifts" of the Prince of Pleasure.
- The Agoniser - Found in the vaults of Occatus I, the Agoniser is a potent and mighty daemon-possessed Runesword. Snaking tubes connect it to a needle in Miriael's arm, where it absorbs the foul narcotics naturally synthesised by the bodies of Champions of Slaanesh. She also wields a daemonic Bolter, another gift to her from Slaanesh for her service as his Champion.
- Tales from the Dark Millennium (Anthology), "The Invitation," by Dan Abnett
- Dark Millennium Warhammer 40,000 Collectible Card Game - Hope's Twilight (2006), Miriael Sabathiel - Champion of Chaos Card (Ultra Rare)