what is the most dark anime on history?

Wow, it's really helpful, thank for your help, I really appreciate it

There are plenty and I can't decide which one has the darkest plot but here are some:
When They Cry
Made in Abyss
Speed Grapher
Lain
Genocyber (Wouldn't recommend this one, its just pure hatred to the world instead of a story or sth)

Personally it has to be beserk 100%

idk but you should definitely read oyasumi punpun

not sure about anime, as for manga prolly punpun

People say monster is up there, but I couldn't quite get into it.

death note is a great anime for this

Death parade is pretty good, about sin and afterlife. I tried to get into Monster but couldn't get into it.

the only i read and darkest is still still full metal alchemist or attack on titan