Srajo "The Obscure", is a legendary White Whistle Delver of the Abyss. Since she is a White Whistle, she is presumed to have made amazing discoveries within the pit and retrieved Artifacts that have changed the world. Like most White Whistle Delvers, she settled on the 5th layer and lived there for some time, since it is the last point of the Abyss where it is possible to return alive.

~!At some point and for unknown reasons, Srajo decided to take her "Last Dive" and descended to the 6th layer of the Abyss without even mentioning it to anyone else. [Bondrewd](https://anilist.co/character/122463/Bondrewd) was the only one that was made aware of her decision.!~

In an age when the corners of the world have been scoured for their secrets, only one place remains unexplored–a massive cave system known as the Abyss. Those who traverse its endless pits and labyrinth-like tunnels are known as Cave Raiders. A young orphan named Riko dreams of following in her mother’s footsteps as a Cave Raider, and when she meets a strange robot when exploring the Abyss, she’s one step closer to achieving her goal! 
(Source: Seven Seas Entertainment) 
Notes: 
- Includes the 4-chapter "How Are You? Somewhere" side story. 
- Nominated for the 11th Manga Taishou Awards (2018).

The "Abyss" is the last unexplored place in the world. Strange and wonderful creatures roam within, and it is full of precious relics that present humans can't recreate. Those that dare to explore the depths are known as "Cave Raiders." An orphan girl named Riko lives on the rim. Her dream is to become a Cave Raider like her mother and solve the mysteries of the cave system. One day, Riko starts exploring the caves and discovers a robot who resembles a human boy. 

(Source: Anime News Network, edited)
 
Note: The last episode aired with a runtime of ~48 minutes as opposed to the standard 24 minute long episode.