Feel free to post or not! Just had to put this somewhere since you conjured up the image with your mer!dunk post.
But Dunk on the edge of mer society, helping others when he can, but specifically helping humans lost at sea and making sure they get back to land safely. All the other merfolk believe it to not only be beneath them but an unnecessary risk of exposing their existence to cruel, ruthless humans.
Then one day, Dunk looks on as a wild sailor takes on an impossible storm, laughing as he is tossed into the depths of the sea. Dunk rushes into the waves to save him, dragging him to the nearest shore all bloodied and delirious, but the man remembers... and he decides he will stop at nothing until he finds the massive man with red hair, eyes the color of the bluest sea and his tail gleaming the deepest seaweed green. The people say he's lost his mind, but the stag will not rest, committing himself to the sea until he finds him again!