Are we allowed to talk about Hentai because that really changes the answer?
But in terms of anime, it seems like theirs a whole genre of anime dedicated to trying to being as dark and shocking as possible.
Madoka Magika and Gantz are probably the darkest of the ones i've watched.
Their are a lot of shows like this that seem really tone confused though.
Like Goblin Slayer starts off extremely dark and f#[email protected]
up in the first episode but seems to really dial back on it after that.
Akame Ga Kill was like a weird mix of every main character gorily dying off one by one game of thrones style..and a shounen/harem/comedy.
Attack on Titan started off pretty dark, but after Eren is revealed to not actually be dead, I realized the show wasn't going to be as savage as I hoped.
And the promised never land is a new series, that's really good and very shocking. But I haven't much of it yet, so I can't tell how dark it's going to get.
Also LOL I googled dark anime and it lists Sonic X as one for some reason.