The Tempest Bride

In the mythology and religion of the Luentials, the Tempest Bride is the mortal-born consort of the sea god, Mytis. It is largely believed that she was a novice of the order of priestesses, called the Deepwater Daughters. Every five years, the novices are offered to the sea god in a tidal ceremony. Of the five, one of these Votaries is taken by the sea. Although they are eventually returned, there is no specific timeframe. They are often found, abandoned, on the shoreline. The girls possess none of their original humanity. They die roughly twenty-four hours after the return to the surface, spluttering nonsensical ramblings and seafoam from their lips.
The myth states that the Tempest Bride is a woman named Neah. Like her paternal aunt, she was selected to be both a Deepwater Daughter and, later, an offering to the god. Determined to control her own fate, Neah went down to the sea the night before her cohort's offering. She entered the waves and called on the god, challenging Him to make a deal with her. Mytis, unaccustomed to being tested, agreed to take her as a Votary. Those left on the surface, knew nothing of the novice's plans, until three of Mytis's previous Votaries were returned from the sea. Inna, once the youngest novice ever to be taken as a Votary, was the only one still clinging to life when searchers found her. Before she died, Inna was able to tell her rescuers about Neah's pact with the sea god and how the young woman had help her trapped sisters escape.

by Brinsmead

The terms of Neah's original offer was simple: if she could find and release her aunt, Mytis would spare a whole generation of girls enslavement beneath the waves. But the sea god was cruel, and had manipulated the terms for His own gain: if Neah could find and release four of the Votaries, he would grant her wish. If she failed, she would have to remain beneath the waves as his Consort, and be forced to handle the fate of the Votaries He claimed.
As only three Votaries were returned, it is believed that Neah failed her challenge. She resides with Mytis beneath the waves, forced to aid in the vicious transformation of the young women taken as Votaries. The selection process continued, undisturbed, at the customary intervals of five years.
The Tempest Bride has never been formally returned to dry land. However, a mysterious creature has been spotted by sailors in the waters of the Gulf of Luentia. It has the appearance of the returned Votaries: a selkie-like beast, who has been known to lead ships out of the path of treacherous storms. It has also been known to approach labouring mothers who, as per Leuntial tradition, birth their babies in special sea baths on the shore. Although she has never spoken, the selky lends aid and comfort to the women before vanishing back into the sea. The Tempest Bride has therefore become a special figure in women's religious devotion, aiding them in the harsh realities of living so close to the vengeful, untamable sea.