Kyber's purge earns Lysander's gratitude and the Duxship, binding the Thirteenth Legion's future directly to his new rule.
Kyber carries out Lysander's initial orders after Hangar 17B, removing people tied to Rhone, Atlas, and the old guard structure while preserving a circle of Praetorians she trusts. Her ally Draconis personally shoots Demetrius, and the visible effect is dramatic: Kyber is the only survivor of Lysander's personal detail whom Pallas can identify after the purge.
Lysander publicly interprets this as rescuing the guard from a Fear Knight coup. He thanks Kyber for restoring honor, promises an end to kill pools and rival cabals, and gives her the Duxship in preference to Gold candidates because she has Praetorian respect and demonstrates that Gray is close to his heart. Kyber calls the Thirteenth Legion a sacred body of the Blood and promises to keep corruption out. Her promotion makes her both the commander of the new guard and the enforcer of the false story on which it was founded.
A lean, unsettling Gray officer in dark armor and blacked-out goggles, standing with trusted Praetorians amid ash and a capital ship's hangars.
Kyber is Lysander's newly appointed Dux, replacing Rhone and consolidating a guard personally loyal to the ruler she believes she saved.