The eponymous 'Siren' of the title, heard regularly all across the town throughout the game's events, is the god's call, compelling Hanuda's residents to infect and immerse themselves in the ocean of red water, thus creating an army of subordinates called . The shibito then go about building a nest to house the god's corporeal form once it is summoned, as well as killing and converting any remaining humans left in Hanuda. Despite Kyoya being able to slay the alien god at the end of the three days the story concludes with only one of the ten viewpoint characters, elementary school student Harumi Yomoda, escaping from Hanuda alive and returning to the real world as she is the only remaining human in the town not infected in some way by the red water.