These 3 are dark not necessarily because of the gore, sex and dark lighting but because the story is a nuanced reflection of humanity's worst side with the constant theme of "humanity is responsible for its own suffering".

Its easy to wave off a group of ugly and no-personality monsters as the bad guys without question but its much harder to come to terms with ourselves being kinda shitty.

I wonder when we're gonna stop acting like Boku no Pico is a scarring experience. It was maybe in in the late 00s, but it's literally just shota yaoi. There is a lot worse out there.