This is an automatically translated description

There are not many unexplored corners in this world. It seems that everything has been discovered long ago. Not this one... a labyrinth of caves called the Abyss. A huge sinkhole, a vertical well full of treasures and unknown creatures. No one knows where the Abyss came from, no one can explain why it is exactly like that.

Those who manage to overcome the endless passages and dips of the cave labyrinth are called depthologists.

The orphan Riko also dreams of becoming one of them, because her mother was one. She still lacks skills, but the news from her mother, who is somewhere deep in the Abyss, motivates the girl to train fiercely. Otherwise, they will never see each other again...

So when Riko meets a strange robot at the edge of the abyss, remarkably similar to a human, she realises that she is one step closer to achieving her goal.