Outlaw: Goro the Assassin(1968)

Overview:

On a cold winter day, Goro Fujikawa (Tetsuya Watari) and Masahiko murder the mob boss of Meishin-Kai. The deed costs them time in prison, but Goro had no shred of regret. When Goro is released 2 years later, Masahiko is dying in prison hospital and entrusts his last wish; "find my sister and take care of her." Goro leaves as a free man with a mission, but soon finds that he might have been better off in jail.