Strait of Embers
Here lies a boiling sea polluted with the ash and Primal Fire emitted from the the Obsidian Arbiter's home. Volcanar's tears protect the his sacred island and prevent most vessels from reaching High Judgement. Those who brave the region's quick trade lanes between the Relic Seas must always remember that they have reserved themselves to the justice of the Divine and his faithful among the native Pa'Nui.
These steaming waters and volcanic islands were once the most beautiful archapeligo in the Realm of Seas until Volcanar began to weep from the peak of High Judgement. For nearly two and a half centuries a near constant rain of burning embers has blanketed the region and polluted it with ash; as all but the hardiest of plants and animals die off, the Pa'Nui are the only Sophonts that have not abandoned their attempts to live in the region. These ancestral waters of the crustean-like insectoids are zealously protected and those seeking passage through the region are undoubtedly forced to deal with one or more Pa'Nui atolls. Somehow, this centralized area remains the spoke around which trade on Marus flows. Whether that be due to traders traveling around its dangers or slipping through its quick sea routes from north to south. Traditional ships on Marus however are unable to travel through the burning rain without damage. Only specialized ships constructed by the Passarins and adapted to the Strait of Embers travel freely. The looming threat of Volcanar is too much for some travelers but he pays careful attentions to deals and oaths made in his dominion, making him an unlikely ally of the area's merchant Passarins. They operate several outposts that harvest Primal Fire to be shipped back to their kin in The Stillness and their efforts to halt its freeze.
I love the juxtaposition of it being such a dangerous place, with embers falling from the sky, but also being a great place for trade because of the oversight of Volcanar.