The story, set on the fictional Rougetsu Island, focuses on Ruka Minazuki, one of a group of girls who was held captive on the island for unknown reasons. Years after their rescue, still suffering from amnesia, Ruka and the two surviving girls return to the island to seek out the truth. The game’s title stems from a ritual mask key to the story. The gameplay, as with previous entries in the series, revolves around the main character exploring environments and tackling hostile ghosts using the Camera Obscura.