"Destroyer of Worlds," by dbschlosser, in Black Cat Weekly, 127.
Tanner is a homicide cop with an enviable record of clearing cases. Unfortunately a lot of that is due to his partner. Not his official partner, but the unofficial one who has embedded herself in his life. Her name is Vishnu or, if you prefer, Death.
Yes, Death, in the form of a beautiful woman, shows up every time Tanner starts on a case. Why? She won't explain. In fact, she says if she told him too much it would mean the end. The end as in, well, notice the title of the story.
I feel like I may be making this sound comic. It isn't. The story is serious and the explanation of what's going on is more logical, less fantastical than you might expect. I enjoyed it a lot.