Oz no Matenrou - Wallpaper and Scan Gallery

Youichi Oonishi and Mari Kudou are private detectives eking out a living by catching cheating spouses in the act and other small stuff like that. Mari's not that eager to work with Youichi, since he's the lover of his younger brother, Miyuki, and also makes passes at him. Their (peaceful?) routine is disturbed when Miyuki asks them to help one of his classmates, Yuu Kaito, who had been stalked by a pervert; after saving Yuu, Mari falls for him but is confronted with a difficult decision when a client asks for Yuu to be assassinated.

Credit: pandemonium91