The Kingdom of the Coral Throne; The Merfolk and the Merlings

The Merfolk are said to be nearly as old as the Avalone, having come to Rysanthis from a world made entirely of water somewhere far beyond the stars,  on a day that can no longer be reckoned.

They are shapechangers who can appear as aquatic beings with the upper bodies of men or women and the long tail of a great fish or, if they will, with a more human aspect, having the form and shape of tall, graceful men and women of great handsomeness and beauty, except that their skin is of hues of green and blue from the very lightest shade to the most vibrant and remarkable hues. All have hair white as snow in whichever form they go about in.

Merfolk usually keep the form of Men, using their fish-like form chiefly for when they travel far by sea or need to escape their enemies in the Deep. The reason they favour human shape is mostly because Merfolk are very fond of taking lovers and spouses--willing and unwilling--from the world above down to their watery courts.

This penchant for fair humans is legendary and has earned them enmity with many of the world of Men, but aside from those kidnapped or enticed to the Sunken Realm, there are two coastal kingdoms in Rysanthis where humans intermarry freely with Merfolk and have a shared culture, the city state of Zimrilas and the Island Kingdom of Haphalla.

The children born of these unions are the Merlings.

Merlings always favour the race of their human parent in appearance, and this is a mystery for the wise to ponder, but though they look mostly like ordinary mortal men and women, they age far slower and, more remarkably, can breathe in water, a trait that can survive as many as three generations among their human offspring. Thus Merlings may come and go between the worlds of Men and the courts of the Sunken Realm.

 Full Merfolk cannot live more than a few hours outside of sea water, which is why their kin in port cities build living quarters which pipe in water from the sea into great vats and tubs to accommodate their sea brothers.

Merfolk live in uncanny rapport with a species of fish known as the Bo'be, highly intelligent creatures which appear as frightening trap jawed aquatic beasts that can inflate their insides with air through a spout. The smallest of the Bo'be are large enough to be ridden as watery mounts by the Merfolk, who can fight upon them when engaging human mariners, making the Merfolk the most formidable sea power in all of Rysanthis.

No human fleet dares ply the seas  for war or trade without treaty and tribute for the Coral Throne.

The Bo'be have the ability to create vast canopies of silvery bubbles brought from the world above down to the coral and stone castles of the Mer Lords, enclosing the citadels and dwellings of the Sunken Realm within vast pockets of continually replenished air, permitting human visitors to that realm to live normally in halls lit by great luminous aquatic plants. The Merfolk build these labyrinthine dwellings near hot spouts and vents which further add to the comfort of their human guests or captives. The Merfolk can swim in the deepests of the deeps but prefer coastal shelves.

The only enemy which poses any real threat to the Merfolk are the terrible and fierce Sea Demons who haunt the canyons and craters of darkness far below the ocean foam.