You shall carry your sibling, be his support and guide.
He shall be your shelter, guardian, aegis firm.
United you stand, divided you fall.
Thie pearly material is also known by the sinister name of Demon’s Tooth.
“A man needs two things to become a saint. He must perform three miracles, and then he must die. Perform your miracles, sir, and come to me when you are ready to become a saint.”
—Azariah Saintmaker, Dread Lord of Hatred
A shape-shifter of some sort has taken up a post at the War College of an enemy realm, where he secretly picks off only the most promising officer cadets, arranging bizarre accidents that gradually debase the leadership of the hostile army. In the long run, this will improve his nation's chances when the inevitable conflict comes.
As a shape-shifter he can impersonate superiors and peers alike and send the target candidate to the cleverly-prepared site of his (or her?) execution. As long as he is successful, no-one will ever know about the deception--even necromancy will only implicate the one impersonated...