English Title: D→A:BLACKTōya and Yuriel are a demon and angel team of soul hunters who go out each night to track down lost souls called Creeps and drag them back to where they belong. One night, the two of them rescue one of Tōya's classmates -- who of course also has a thing for him -- from a Creep, and she finds out his secret. Serious romantic/creep/Creep shenanigans ensue.
Japanese Title: ディーエー:ブラック
Publisher / Developer: Tonkinhouse
Genre: Visual Novel
Released: Dec. 25, 2003
Product Codes: SLPS-25288 / JAN 4961355677834
The first in the two-part D→A series, this is what can only be described as an "action visual novel". Most of the game is your standard anime stills with voiceovers, but certain decisions have a time limit (and not answering at all has its own repurcussions). There's also real-time battle scenes that play out like a rail shooter.
I haven't yet played this, but it's fairly well-regarded in Japan. This version is the limited edition, which comes with a bonus DVD that's mostly developer diaries and voice actress interviews. Character designs are courtesy of Murakami Suigun, who is best known for his adult game work.