Ok, so that last one wasn't quite what I was looking for. Maybe I could try a manga combining vampires and crime fiction?
BLOOD ALONE, by Masayuki Takano. First published in 2005 and first published in North America in 2006.
PLOT:
Misaki seems like a sweet, polite girl. Her partner, Kuroe, is much the same. You'd never guess that sweet little girl was a vampire or that Kuroe is the survivor of a vampire attack. You'd certainly never expect these two to be part-time investigators who use their connections and powers to solve the crimes that are beyond the capability of the police.