An enormous cave system known as the Abyss, is the last unexplored place in the world. No one knows the depths of this titanic pit, inhabited by strange and wondrous creatures, full of mysterious ancient relics whose forgotten purpose has yet to be rediscovered.

Generations of bold adventurers came to be known as "Cave Raiders", all drawn by the cryptic depths of the Abyss.

In Oosu, the town at the edge of the Abyss, lives an orphan girl named Rico who dreams of becoming like her mother: A great Cave Raider determined to solve the great mystery of the pit. One day while exploring its murky depths, Rico stumbles upon a little boy, who she discoveres is a robot.

Note: Nominated for the 11th Manga Taishou Awards (2018).