Last Client 

The story is about a young male prostitute named Aya and a former assassin named Chris. Aya's father murdered his mother in front of him, then forced him into prostitution. Since that time, he has always been looking for a way to inflict his revenge. Chris is just that method. After Chris saves Aya from his pimp, they form a fairly deep friendship, and Chris decides to make Aya his Last Client. A classic yaoi story.