Possible Clues:

• Japanese spy or assassin
• Teenage Mutant — Turtles (TV/film)
• Black-garbed mercenary
• Martial artist imparts physical damage (top half) during an uprising
• Martial arts movie figure
• Trained assassin in prison in Japan
• Some man in Japan's a killer
• Assassins concealed by curtain in Japan
• Dark-clad warrior
• Master of concealment, part of tradition in Japan