the traders of the Underharbor exchange many different types of wares to the people of the Rainy City. Foods include fish, kelp, sea cucumbers, eels, shark meat, snails, crustaceans, and many other sorts of underwater creatures. They also trade shells, pearls, coral, rare fish, sunken treasures, and any other sort of thing air-breathers may be interested in. There are also unsavory merfolk who will trade in darker things, such as the bloated corpses of the drowned for necromancers, poisons harvested from sea urchins and other dangerous fish for alchemy (to anyone who will pay well for it), semi-intellectual humanoids (sea-monkeys), and any other sort of service the seedy side of the city may be interested in (the “drowning” of certain ships for example…)
There used to be a king that ruled the Underharbor with a beautiful trident made of coral as a symbol of his status, or so they say. The name of this king, who his successor was, and the trident were lost in the waves and the confusion of many different races congregating under the shadow of the rainy city generations ago, but that does not stop different prominent families of merfolk and other races from claiming they are descendants of that legendary line to this day. For the most part the Underharbor is ruled by a couple of rich and powerful families, other creatures and less wealthy merfolk are employed by these families no only to undermine each other, but also to fight against the common goal of the undead that bombard the boarders of the watery realm.
Other Things to Consider-
Just like most of the people of the Rainy City, most of the inhabitants of the Underharbor migrated/drifted here from other seas when their homes were destroyed. When waters get too high sunlight does not reach the floor and vegetation dies; when that happens animals leave, and people have little to sustain themselves from. When these worlds die, the sea engulfs all the runoff, pollution, and debris and themselves become churning, poisonous, uninhabitable places that must be left behind. While underwater inhabitants do have an advantage being that their world is wet, the Rainy City is not where most of the inhabitants of the Underharbor want to be and many long for a world with sunlight, clear water, and warmer currents.
The Seas beyond the coast of the Rainy City drop off suddenly. Where the water turns dark one knows to turn back; the Dark Water harbors dangerous beasts, untold horrors, and unpredictable weather, making it a suicidal decision to swim out where the sea cliff drops to untellable depths. Only the mad, and the suicidal venture out to these waters, and never return to tell the tale…