I liked anime adaptation a lot, the world of the Abyss was like a breath of fresh air in the sea of isekais, but manga is straight up disappointing. Author shows no intent in developing such a rich, beautiful setting into something more than a pretty decoration for suffering of useless lolis. The latter is especially annoying, it's almost like the success of Mitty's arc made him realize that torture and murder of cutesy characters will always emotionally shatter certain kind of people and from now on he does it again and again, til the point it gets tiresome and boring instead of shocking and sad. I'm not going to hate on this manga for violence and sexualization, it's just not very well written story. Main characters are barebones, boring, cliched "good guys", especially Reg, who is the most shallow overprotective white knight trope you can imagine, side characters don't contribute a lot, they are either: victimized loli punching bags or walking lore dumps. Some plot lines are just ridiculous and super rushed (everything about Prushka) or outright bad (Mitty 2.0). Characters can do as much mistakes as they can and still be saved by armor and their needs will be fulfilled in one convient way or another.
I expected adult story about children, I've got children's story with adult content. Beautifully drawn, tho. I've read somewhere that author worked as concept artist in Konami, and, yeah, he is great when it comes to designs and concepts (relics descriptions, monsters, setting details), but the story and characters are certainly lacking depth (no pun intended).