(Average+) Angels of Death

Series in one sentence:
I love y.. I mean.. kill me, you promised.

Series in more sentences:
Rachel ends up in a strange underground location after her parents were murdered and she lost her mind. She finds out that the place is far from safe and houses a small amount of serial killers, each given their own floor to rule over.
When the girl regains her lost memories, though, she comes to the conclusion not to deserve life anymore and manages to strike a deal with one of the murderers, Zack: She'll help the simple-minded criminal escape to the outside world, if he promises to kill her afterwards.
 

What to think of this one.

It was like I was watching an alternate reality, one where people are unrealistically evil and insane murderers are considered "pure angels". Where wanting to die and someone willing to answer to that is an act of true love.. But then the last episode kicks in, and it becomes clear we're dealing with the real world. So then, how come some of these characters have superhuman strength? How is it possible for characters to keep cheating death? How does it explain all the magic elements we've witnessed episodes prior? It's never explained.

Nevertheless, it's an interesting anime, I enjoyed the two main characters for the most part. It was cool seeing these two opposites joining forces getting through the puzzles set for them, but every time I allowed myself to believe that their relationship was growing into something charming, they say some dumb bullshit that tells me I'm wrong. 
I love how they interact, but on the other hand, the way they express their "like" for each other is messed up. Not once have they expressed themselves in a normal human way and they always seemed to be dancing around the subject.
Whenever a character in the show asked either one of them about the other, they always replied with something like "Well, I want to die and he promised to kill me, that's why I want to save him!" or "I never lie and I promised this girl to kill her, that's why I want to save her!".

What the fuck kind of script is that?

Why can't either one of them say "I've grown fond of you, we complete each other, I'm no longer lonely, bla bla"? Why is their tight bond always referred back to this moronic promise of death? It makes their otherwise cool friendship totally pointless. Fake, even.
Also, for a girl who wants to die so badly, Rachel sure resists alot. Even when Zack is seemingly about to kill her, she resists. Because of reasons. Messy character arc in this one. If the story doesn't actually want her dead, then why does everything revolve around her wanting to die?

I think Zack and Rachel aren't people we, the viewers, can understand. Maybe that's the point, they're insane, not meant to be understood by normal folks. But why then have us emotionally invested in their relationship? This is obviously what the anime tried to have us do.
You can write two fictional characters to be mentally insane, but still able of showing signs of humanity, thanks to having each other. But having Zack doesn't "cure" Rachel from her wish of wanting to die, and Rachel doesn't "cure" Zack from wanting to kill her/people. So again, what is the point of their relationship?

The anime could've also gone without this God, angels and death nonsense. I didn't think it had a place in the story.
A story about an eccentric rich dude who collects famous murderers as a weird hobby would've been better, opposed to some priest locking himself up with serial killers because whatever the reason even was..

But alright. I think it's worth the watch, but be ready to sit through shit excuses from the characters and a lacklustre ending.