If you've watched Darker than Black, you'll recognize the spoken lines that open the ... er ... OP. "Now I’ve lost it; I know I can kill; the Truth is [something] beyond the Gates." I'm not too familiar with the horror genre, so this may just be a classic horror-type voice, but the association I make goes to a completely different place.
The voice is awfully reminiscent of the first bit of "Sing Me A Song Of Songmy", a collaboration between Freddie Hubbard and İlhan Mimaroğlu that is one of the most insane things I have ever heard, if not the insanest. The first minute is a layered mishmash of spoken word, violin, and "tape"-type electronic music. The spoken word is delivered in a strangely intense, declamatory manner, and the phrases are both baffling and chilling:
"Give me love. Give me love so that I can ... kill."
"He made me feel that I could play the guitar."
"I feel like I can hold a knife."
"We am. I are."
There's a lot more, these are just a few. After that craziness, the work falls into a more straightforward jazz feel for a while, and then goes all over the place. Overall, it's an anti-war work, and thus probably has little to do with Darker than Black (though the story in episodes 5 and 6 hints at that direction), but I wonder if the people who made the OP had this work in mind.