

Angels of Death

Most girls waking up without any memory and meeting a serial killer would panic, but not Rachel. In fact, far from being her biggest problem, killer Zack might just prove a convenient resource when it comes to finding a way out of the building in which they're both trapped!
You need to be able to take quite some brutality.
While I think they could have easily ejected some story scenarios, and there were quite some questions unanswered throughout the anime, I think the ending comes with an interesting statement:
[spoiler]No matter who you are, you will always be a human.[/spoiler]
I felt that single statement, given the characters, was incredible simple and deep at the same time, and sends an important message. It was absolutely impactful for me.