The Primarch watched.
At the very bottom level of the flagship, an Inquisitor named Eisenhorn stood with his hands behind his back, interrogating a prisoner captured during the war.
An Eternal War Veteran of the Black Legion.
After roughly forcing the veteran to recall certain events from his past, Eisenhorn turned and left, but he left something behind in the interrogation chamber.
It was a strange brass-colored box.
The moment he saw it, Sanguinius suddenly realized that the box was called the Box of Mourning.
The Box of Mourning had been created in humanity's primitive age. At the time, shamans from several human tribes on Earth had joined forces, intending to create an object that would ensure humanity would never lack food, warmth, or happiness. The object was eventually forged, only to be lost.
Sanguinius had never seen this thing before, yet he knew exactly what it was. He also knew that Eisenhorn carried it because it possessed the power to seal demons and souls.
Eisenhorn had acquired the Box of Mourning in his youth during a rebellion-suppression campaign against a planetary Governor who had fallen to Nurgle. Back then, his retainer Bekun had used the box to seal the ascended Governor, and Eisenhorn had kept it by his side ever since.
"Dangerous," Sanguinius murmured.
He realized that the Box of Mourning was not actually meant for sealing demons.
A person with a pure soul could indeed use it to seal demons.
But if an ordinary person possessed it, they would only unleash something terrifying.
Yet because this was a prophecy, Sanguinius had no way to intervene immediately.
Unaware that he had lost the box, Eisenhorn walked away.
Another Inquisitor from the Daemon Inquisition noticed the Box of Mourning. He picked it up, and after probing it with Psychic Power