The Borderliners

The Borderliners summary:

After being gruesomely murdered, Park Juhyeon begs the grim reaper for a chance to find his killer. To solve this mystery, he returns to earth as a ghost and teams up with Choi Seongmin, a vampire who assists the dead in the world of the living. As they dig deeper into the case, Juhyeon uncovers some disturbing clues and slowly realizes that his past was less clear-cut than he remembered. Was Juhyeon really just unlucky to meet an untimely death? Or did he have a hand in his own bloody demise?