The Sea of Suffering is a cosmic expanse referenced in the canon as a reservoir of souls that have suffered beyond death. It is one of the darkest background concepts in Shadow Slave cosmology.
Link with Defilement
The Defilement — corruption initiated by Aletheia after her passage through the Tomb of Ariel — seems to feed on or echo within the Sea of Suffering. Defiled creatures (corrupted versions of Nightmare Creatures) carry its mark.
Dark Magics
Some magics — those tied to Ariel and the Demon of Dread, and the corruption associated with the Sin of Solace — tap into or draw from the Sea of Suffering. The bearer pays in sanity.
Canonical Note
The exact term 'Sea of Suffering' appears mainly in sybil murmurings and cosmic visions. Its exact nature (metaphysical location or poetic metaphor) remains ambiguous.