The"Abyss" may be the last haunted place, a massive and dangerous cave system full of ancient relics and strange creatures. Just the bravest of adventurers can traverse its own flames, making them the nickname,"Cave Raiders." Up on a robot that resembles a boy, a girl named Riko stumbles within the depths of the Abyss. Tantalized by the Abyss, her new friend along with Riko descend into uncharted territory to uncover its mysteries, but what's in wait for those in the shadow?