Death Note is fairly dark, Gantz is disturbing
Death Note I have read and watched but Gantz I will check out Thanks (▰˘◡˘▰)
Zankoku Na Kami Ga Shihai Suru is one of the darkest to me. It is tagged a yaoi but to me its not because of all the fucked up psychological and physical abuse going on to the main character. You don't for one second think of it as cute/fluffy/smexy or whatever. Definitely not for the faint of heart if you ask me.
Gantz is something...but theres Junji Ito's work. My favorite one from his was Uzumaki. Fetus collection by Kago Shintaro was a bit twisted
Junji Itou's collection tho
The darker, the better. The plot reminds me of 'Kokoro O Korosu Houhou' which I am currently reading so guess I'll be reading this too..thanks :)
parasyte is a good one.
Harada-sensei
Lol i was gonna say that
Zankoku Na Kami Ga Shihai Suru f*cked me up mentally and physically. I'm just gonna add this one: http://www.mangago.me/read-manga/mr_arashi_s_amazing_freak_show/
The darkest manga you have ever read...the kind makes you have brain gymnastics. Like Moritat!