The core had inside Cassian for a while but it still wasn't his.
Not yet.
The moment Cassian crossed the Sovereign threshold, that distinction would disappear. His soul would seize the Death Core as the foundation of his Authority.
The accumulated Death Aether would cease being stored power. It would become Cassian Renault's Divine Authority of Death.
A new Sovereign.
A new owner.
Klaith would no longer be able to simply remove it. Even killing Cassian afterward wouldn't solve the problem easily. Once Authority formed, it became anchored to identity.
Breaking that bond could damage the core, scatter the accumulated Death Authority or create an entirely new inheritance because the current core contained the former death Sovereign Authority.
Worse, a new Death Sovereign might awaken things Klaith didn't want awakened yet.
The seal itself could respond, the ancient remnants could notice, and the being Klaith intended to restore might reject a core branded by another Sovereign.
