A man suffering from anterograde amnesia as a result of a violent attack in the past sets out to avenge his girlfriend's death with the aid of photographs, notes and tattoos all over his body.

A westerner named Casey, studying Ninjutsu in Japan, is asked by the Sensei to return to New York to protect the legendary Yoroi Bitsu, an armored chest that contains the weapons of the last Koga Ninja.