She is a creature of the sea, and the sea is inhuman. Its waves will toss and turn, foam churning atop the white-brine of the water. It roars. It wails. It scrapes the salt on the tips of its thousand shapeless fingers against the gaping wounds of sailors, of any man caught in its depths, pressing close to the bloated corpse like a lover, sinking inside its lungs. It is cruel without knowing the rules of cruelty and this is part of how it loves.
There is little of the inhuman inside her Achilles. Enough to make him beautiful. He is a light thing and stands small before her when she comes to see him on the shore. She looks down at him with her cold, cold eyes and is curious about what kind of creature he might be.
Not human, of course. He is hers. She has made him - her blood is what makes him strong. So he is like her, perhaps; his eyes remind her of the sun through the surface of the sea, his hair, the glint of scales, the soft line of his mouth curving like the waves when the wind is gentle and the water is calm.
But he steps into the tide and does not melt into it. So she watches him, and she is silent, and she is still amongst the rocks. He kneels in the sand and spends hours sifting through it. He climbs into the low-hanging trees and loosens into the swell of its branches. Mother, he does not say to her face, but he tilts his cheek into the tip of her claw. He does not blink.
Her child leaves when the morning comes, the sun lighting his hair, seabed pale and soft as down. He makes his way back to the human world, his regular migration to the place where he sleeps when he does not come to her. He is still young, but the grace of ethereal things is innate to him and he slips away through the grass, heron-fast and swift. Her bird-child. Fledgling.
She thinks. Birds do not live long. They are sweet-voiced and pleasant, with sharp, gleaming beaks. Plumage in all the colours of the sea and sky and earth. Plumage in all the colours of fire, that thing that was stolen from the gods. Her bird-child.
A bird will die quick. But there are the fire-birds, and they will live forever. They are unmade in a blaze, and made again from the ashes, immortal and radiant and everlasting. They will never touch the sea, the fire-birds, but to see them over the horizon is close enough.
Her bird-child. She will make him a god.