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Berserk" is dark and gritty.
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Hellsing" is dark and occult. The protagonist is called Arucard and for a good reason.
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Aoi Bungaki" has dark,depressing and bitter sweet stories. It's basically an anime version of (arguably) the best Japanese novels ever written.
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Basilisk" is another dark and gritty anime. I personally liked how the story unfolded, it felt like an old-school play.
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The Count of Monte Cristo" is the alternate universe anime version of the (french?) play/novel(?) of the same name.
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Elfen Lied", which is touted as being the goriest scenes in anime.
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Afro Samurai" and it's
sequel. A good contender in terms of gore with the above. It also has some of the best animation I've ever seen.
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Ergo Proxy", a dark and philosophical sci-fi.
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Kara no Kyoukai", a dark anime consisting of 7 films. So the animation and stuff are excellent (cause you know, film = highbudget).
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Kurozuka", you'll probably be confused the whole way through but when you reach the end your mind will equal blown.
I assume you're a fan of sci-fi, if so you'll really like "
Memories". It also has black comedy.
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Mnemosyne", violent and gore filled. Has awesome action. Consists of six 45min long eps.
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Monster", it's a thriller. Has arguably the best story of any anime.
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Paranoia Agent", contains paranoia and
excellent music.
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Seikimatsu Occult Gakuen", contains occult stuff, as the title states.
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Shigurui", a work of art painted in blood. Nuff said.
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The Animatrix", shows how the robots came to power. Contains metaphorical buttrape (for the humans).
Oh and for teh lulz, "
Detroit Metal City". It's a comical take on death metal.
Another one for the lulz since you're into politics and all that jazz, "
Hetalia Axis Powers", it's a comedy.
And the stuff the others recommended.
Which I'm cool with.
but they will never change 