John Rain books by Barry Eisler

Rain Fall
John Rain was born of an American mother and a Japanese father, Rain is a businessman based in Tokyo, living a life of meticulously planned anonymity. Trained by the U.S. Special Forces and a veteran of Vietnam, he is a cool, self-contained loner—and he has built a steady business over the past twenty-five years specializing in death by "natural causes." He is also a man struggling with his own divided nature: Japanese/American; soldier/assassin; samurai/ronin. He is given an assignment to kill a man on a train but to make it look like a heart attack. When he notices an american man going through the dead man's pockets Rain's carefully ordered world begins to unravel. Unknown agents from within and without the international intelligence communities have been circling him for years and, having connected him to the subway job, now have the scent they have been seeking. At the same time, Rain is drawn outside his private world by an alluring jazz pianist, the dead man's daughter, who is the key to the very secrets that her father died trying to reveal.

Fascinating read. You really get a feel like you are in Tokyo and walking beside him. Looking forward to reading more.

Hard Rain
Rain Storm
Killing Rain
Last Assassin