I'm the Grim Reaper, Vol. 3 (manga)

While foiling an attempted robbery, Scarlet is forced to reveal her role as a grim reaper in order to save Chase’s life. In return, Chase shares some of the past events that earned him his sinner’s mark, and together they embark on a new kind of partnership - instead of killing sinners at random, they will use Chase’s experience as a detective to bring only the worst sinners to justice. But even seemingly moral choices have their cost, and Satan isn’t the type to share his reapers with anyone else…