Ilim is one of the children brought down in the depths of the abyss by white whistle Bondrewd, together with Mitty and Nanachi. Later on, it's highly likely that she is one of the Narehate seen in the sixth layer of the abyss.

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.

__Nickname:__ なっちゃん (Naa-chan)

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A compilation film recapping the second half of the anime series. 
 
The mystery surrounding her mother’s death deepens as Riko learns more about the truth of her origins. More determined than ever to travel to the bottom of the Abyss, Riko and Reg leave Ozen’s Seeker Camp and delve into the treacherous Third Layer — and beyond. 
 
(Source: Sentai Filmworks)