7 years after the tragic fire that took her parent's life, 17 years old Luna lives a simple and quiet life on the Scélène island, along with her adoptive family: Father Heide, the chief priest of the village and his energetic daughter Myrthe. On the crescent shaped island, each villager has to abide by the words and desires of their savior, the Scarlet Goddess, and her Envoys. If they wish to survive, they have to pay the price of their ancestors's sins, and repent with their own blood. Only once a year, the Envoys of the goddess would come to the island for the Festival of the Scarlet day. During it, the chosen ones among the villagers would join their ranks, and venture outside the dome of fog that protects the island. But it has been years since the Envoys' last visit, and most of the villagers do not expect they will come back. That is, until Father Heide receives a red letter announcing their intention to attend their first Festival in 7 years. Soon, strange events start to occur on the island. Along with the appearence of a mysterious stranger, Luna's nightmares get more vivid, and Myrthe's ambitions put her in mortal danger. In the midst of the Festival, will the sisters uncover the secrets of the Scarlet Moon, or will they get swallowed by it before Dusk ?