Báiyù

Baiyu was born with a white jade gem on her forehead, giving her her name. That was the sign of a blessing from the gods. 

In her hometown, every 21 years a blessed child would be sacrificed to bring wealth to the land, and a new one would be born.

Baiyu escaped her fate and made a new life for herself in a distant seaside village. Eventually the leaders of the hometown found her and tried to bring her back. While fleeing, Baiyu fell down a cliff and died, her body sinking into the sea.

She was reborn as a mermaid, finally free from her predetermined fate.