Arianna, a noble maiden, is betrayed by her clan and offered as a sacrifice to the deep sea. There she meets Calian, the sea god trapped by his ancestors for a thousand years.
Suspicion slowly blooms into mutual redemption between them. Together, they uncover the Walden family’s millennial secret: they slaughter sea folk and harvest their magic for profit.
Facing the villain corrupted by the Siren’s Heart, the human girl and sea god rally the sea clans to stop the apocalyptic ocean disaster. Arianna abandons her noble title, ruling the boundless deep alongside Calian.
