After wjs018 mentioned the adaptation - Heavenly Delusion - in an anime thread last week, and more specifically after I looked it up and discovered that the original manga is by Ishiguro Masakazu, I binged Tengoku Daimakyou.
Ishiguro Masakazu is the author of one of my all-time favorites - Soredemo Machi wa Mawatteiru. It's a fairly straightforward SOL with a particularly good cast of characters, but it also has a certain amount of overt weirdness scattered here and there.
Tengoku Daimakyou is pretty much exactly the opposite - a thoroughly bizarre and brutal post-apocalyptic mystery with a certain amount of SOL scattered here and there.
In part it's post apocalyptic SOL in the vein of Girls Last Tour or Usuzumi no Hate, as the protagonists explore and try to make sense of the crapsack world in which they've found themselves. But mostly it's a bizarre mystery thriller alternating between the story of the two protagonists in the outside world and the "students" at a sinister research institute, and the odd connections and overlaps between them.
It's ongoing at 63 chapters currently, but feels like it's getting near the end, since there are only a few mysteries left to be cleared up. And it's terrific and highly recommended. And I'll be linking the new chapters here as they come out.