Caenis

The nymph Caenis was walking along the beach when she was seized and kidnapped by Poseidon, god of the sea and a notorious girl collector. After raping her, Poseidon promised to grant her one wish. Caenis asked for what her heart desired most: to change her gender, so she would never be raped again.

Poseidon was furious about this wish, but because he was a god, he could not take back his oath. He turned her into a boy. After which Caenis changed her name to Caneus...

Ocean by Engin Akyurt.