Shut hell
Hellsing
Akame ga kill
Well I mean those are the ones that thoroughly disturbed me but I still read them all... (except for elfen lied)
these all have wicked protagonists and they're quite dark:
http://www.mangago.me/read-manga/drag_on_dragoon_shi_ni_itaru_aka/ (gore warning. I felt like there was no plot in this so I don't recommend it)
http://www.mangago.me/read-manga/adu_of_hades/ (this is awesome. Plot twist in ch. 1. I'm writing this cause I started reading from ch. 3 and the twist got spoiled for me)
http://www.mangago.me/read-manga/yakushoku_distpiari_gesellschaft_blume/ (plot twist in ch. 3. Don't let the cute art fool you)
http://www.mangago.me/read-manga/fire_punch/ (this is awesome. first chapter is enough to show what a fucked up world they live in. MC isn't wicked, he just wants revenge)
"ib - instant bullet" but it's just too depressing. I didn't read it.
http://www.mangago.me/read-manga/sekai_oni/ This one is a little creepy and disturbing. psychological manga. sketchy art.
I know more but they're supernatural or death game kinda stuff. or like Prison Lab.
http://www.mangago.me/read-manga/ibitsu/
http://www.mangago.me/read-manga/sprite/
http://www.mangago.me/read-manga/funouhan/
http://www.mangago.me/read-manga/conductor/
http://www.mangago.me/read-manga/book_club/
http://www.mangago.me/read-manga/toshi_densetsu/
http://www.mangago.me/read-manga/ibitsu_no_amalgam/
REALLY CREEPY, DARK, BRUTAL FANTASY MANGA?? (I've already read Berserk and Claymore) thank you!! (●'◡'●)ノ