In an era when the corners of the world have been searched for their secrets, only one place remains unexplored - a vast cave system known as the Abyss, filled with terrifying creatures and lost relics. Those who dive into its depths are called Cave Raiders. A young orphan named Riko dreams of following in her mother's footsteps as a Cave Raider, and when she encounters a strange robot while exploring the Abyss, she is one step closer to achieving her goal!