I don't tend to watch eroge shows very often any more, but I'm hopeful this will at least be interesting. I like Mashimo's more pretentious girls-with-guns shows (didn't like El Cazador, it was too normal!) so I'll give this a shot.
I'm really only here to go:
i) Hikaru Nanase music!
and
ii) Holy crap the OP is beautiful! It's called "Karma", and it's sung by KOKIA who specialises in weird trippy music. You can hear a clip of it at
this Spanish language website from a radio broadcast. I can't wait to see what Mashimo and co. do with the animation on this.