Just watched Made in Abyss.
Oh god. It's surprisingly good. But I have to warn you, it looks like a sweet and innocent anime. But it gets dark. Really dark.
Like body horror, Full Metal Alchemist Elric brothers resurrecting their mother, shoot Old Yeller because has rabies - kind of grim tale. It's definitely for mature audiences. Creepy sexual undertones, nothing as extreme as Neon Genesis Evangelion's "I'm so fucked up" scene. But the characters are suppose to be preteens, only they look like kindergarteners, and you just know the show is playing at all types of fetish fuel.
So to give you a quick premise without spoiling anything, there's this society built around a pit called "the Abyss". It's basically like those Tower/dungeon rpg based animes, like Tower of Druaga, and Danmatchi. The pit is full of monsters and relics, and these people excavated it. But it doesn't have the RPG party cast. It's an orphan miner girl and a boy robot. It's got similarities to Cave Story I guess (I've never played it). Some people compare it to Dante's Inferno and it's levels of hell, but I wasn't picking up on any deep spiritual symbolisms or parallelisms.
Besides being dangerous the deeper you go, coming up is also an issue because of a "curse". Almost like divers decompressing. At some levels it's just dizziness and nausea, deeper it causes hallucinations, bleeding orifices, mutating, and death. These hit once you begin going up a slope or any kind of ascent.
Anyways, girl finds mysterious robot boy with no memory. Girl's mother was a prestigious explore who reached the deepest depths. Mother is presumed dead but a message suggests she waiting at the bottom of the abyss, with a possible connection to the the robot boy. The girl and the robot boy go down to look for her and some answers.
A lot happens in 45min episodes. 13 total. Worth a watch.