River Styx Contract

When the River Styx had first begun spreading through the Underworld, Ropus, the Underworld's nominal master, had not intervened to stop it. The River Styx was a product born in accordance with the will of the Underworld; even if he had tried to stop it, he could only have slowed its spread. As a higher god, Ropus understood this well and thus paid it no mind. In any case, even if the River Styx's power became part of the Underworld, it would not affect his own power or his rule over the Underworld.

Carceri, however, was different. As the lowest level of the prison, the Dead Nether Prison layer was a domain under Naraku's control.

Naraku was a mad god of death, while Ropus, the God of Death, was the god of the Underworld,...