In days past, Nerida saved the gravely wounded Kyle, and the two fell in love—and because of the pact, they lost their mermaid marks. Jealous Leona colluded with the sea demon, used dark magic to tamper with Kyle's memory, falsely claimed the debt of gratitude as her own, and framed Nerida as a sea demon. The amnesiac Kyle subjected Nerida to every kind of torment, and planned to sacrifice her to the heavens at the full-moon festival. At the critical moment, the guard Seren helped Nerida reveal her true form and break through the memory seal—she faked her death and turned into foam, while Kyle, guarding the mermaid's tear, was left to regret it for the rest of his days. Nerida narrowly escaped back to the deep sea, but because of the pact she was afflicted with a poison curse, curable only by the blood from Kyle's heart. Disguised as a holy maiden, Nerida, accompanied by Seren, returns to land to begin her bloody revenge.
