In a world illuminated by four suns, one suddenly vanishes, plunging people into despair. Cheerful, tanned sky explorer Naia and her elegant automaton companion Mano set out aboard their airship to investigate the legendary Tower Shrouded in Mist, said to be where the lost sun fell. A fierce storm damages their vessel, forcing them to land inside the massive tower. While repairing the ship, they explore its ever-shifting labyrinthine interior — only to encounter hordes of bizarre monsters and vengeful spirits. Naia is quickly overpowered and captured by Mary, a laid-back yet ruthless ghost maiden who rules the tower and shows no mercy to intruders. This marks the beginning of their dangerous, seductive, and highly erotic adventure deep within the mysterious tower.