I like Senketsu no Elf (painfully enough, the only volume that was translated please translate it hint hint, I can edit it), and Bluesteel Blasphemer. Please give me more of the same. Make my onion water flow.
Ouroboros Record ~Circus of Oubeniel~ has a truly villainous MC. It has human experimentation, brain modifications, brainwashing, mind breaking(not in a sexual way, more like losing sanity) and so on. Dark enough?
http://www.novelupdates.com/series/tower-of-karma/ http://www.novelupdates.com/series/the-lazy-king/ http://www.novelupdates.com/series/summoned-slaughterer/ Watch Goblin Slayer manga or find epub's.
https://eternalpath.net/steal/ Used to be on RRL but too many people bitched about the dark content so he deleted it there and quit, still a good read for the most part.
If ypu want darkness close your eyes.ahahhahah Kidding if you want darkness then i recommend youji senkai
I second this. Would have added myself if it weren't there. It is brilliant in a twisted way. Also, outside of novelupdates, read 1984 by George orwell. I can't praise this enough.
Dystopian novels fit "darkness pretty well". Once you've got through the NU recommendations, I'd recommend you try stuff like 1984, Fahrenheit 451, Brave New World and The Running Man. There are some good ones you can watch too e.g. A Clockwork Orange, A Handmaid's Tale and Metropolis. (Metropolis has an anime film too).
Demon Girl ~Tale of a Lax Demon~ - Dark fluffy Arena - can get dark and sad at times Please make your reading list public
1984 is a fantastic book. It really opened my eyes to classical books; I cannot recommend it enough either. Making my reading list public means actually updating it. I'll need to do it sometime.
Nidome no Yuusha Main Character Hides His Strength Instant Death Have you watched Akame ga Kill ? I think that's pretty dark