A While back I was divided on what the equivalent of Princess Andromeda and Cetus, the sea monster she was sacrificed to, and the answer ended up being that they are one and the same.

Xia was born a Monster, and the only child of the the King and Queen of an independent “city-state” on the water (kinda like if somewhere like Boston became its own nation and a monarchy). Her parent’s were terrified that their one decendent is essentially a whale, and begged to Neptune if there was any way he could make their daughter human. Neptune agreed, only if they made him the City’s Patron God.

Since turning a born-monster into a regular human is beyond Neptune’s capabilities, he instead gifted the princess with a “false body” that she possesses. When Xia (the monster) falls asleep, Xia (the human) awakes and vice versa, one half feeling like a dream to the other. Much of her childhood she was not explained this by her parents, and wondered whether she was a human who dreamt of being a Monster, or a Monster dreaming about being human.