Amongst the choirs of the 9th, the Exousiai were a caste of Assault Marines known to exemplify the high intensity warfare practiced throughout the legion. Squad Ahdriel (thus Exousiai Ahdriel) were a band of Assault marines honoured with the role of Lamenter. When Blood Angel lives are lost in the service of the great crusade an honour guard is left stationed at that world. These Lamenters were spread across the breadth of the galaxy by the time civil war broke out, a resource the scattered IXth could not ignore.
Lamenter Ahdriel was a morbid presence within the ranks of the IXth, made ever more bitter by Horus' betrayal. This Choir of Exousiai was rescued by the 133rd, tracking a larger Iron Warrior munition fleet.
The Heresy war took a heavy toll on the Exousiai, equipped as they were for xenos and light infantry purgation protocols. They found themselves woefully ill equipped to tackle Legion forces and suffered a high attrition rate throughout the rebellion. Archive photographs shows us varied range of armour marks throughout Exousiai Arcellus with battlefield scouring of the dead being a common practice to replace damaged equipment.