^ my god this comment, I can't even #spill that tea mister.
As for the topic..
1) Corpse party - the anime itself wasn't as scary as the mangas and video games but it was one of the first horror ones that stuck to me.
2) School Live - is actually more of a psychological one in a way but horrific still
3) Akame ga Kill - the anime wasn't that disturbing at all but if you read the manga... ouch is all I can say
4) Higurashi - the animation and art style made it more horrific than the manga LOL
5) Another - umberlla ella eh eh eh..if you watched it you'll get it :x
6) Deadman Wonderland - got me shook on many many levels
Other than that Shiki, Promised Neverland, Psycho Pass, HxH is pretty messed up as well in all honesty...going to throw in Death Parade ans Hell Girl as well.
Sorry for the list, maybe I get easily affected by such genrea gwnre but I have vivid memeories of them all
I'm not sure, but I think that Ninja Scroll was one of the darkest anime I have seen
Inaka Isha~I was also scared by my ignorance...
Devilman's OVA!!!So amazing and slightly gruesome!Tha mangaka's style hah.I was a big fan of gruesome and dark stuff some years back hah...
Corpse party is terrifying. specially the games. Though like higurashi its more horror, jump-scares than really dark imao. I've read akame ga kill and deadman wonderland and they are extremely dark on every level. I haven't got to the promised neverland yet but ive heard, dark dark things about it, though everyone who tells me about it is extremely vague as though hiding some secret. Death Parade wasn't really scary but at its core it delt with some pretty dark concepts.
I like your list.
So far, Higurashi no naku koro ni
Trying to break the fourth wall? Pretty accurate description of maiotaku. But is this the darkest animu? Nah, not really, more like a comedy if anything else. There are a lot darker sites then this for anime. From my own perspective this site has a bunch of overly emotional, easily offended, angsty kids.
Judgmentoftherain~MaiOtaku is dark because members more or less have their issues;however compared with comments sections of many other websites/forums, MaiOtaku is so entertaining...At least, most active members are kind and timid people who don't really like hurting others~