Tako kot v času samurajev tudi zdaj še vedno velja, da ninja Koga poseduje orožje z legendarnimi močmi, ki lahko premaga tako dobro kot zlo. Smrtonosno orožje je zdaj zaupano ameriškemu študentu Caseyju, ki na Japonskem študira umetnost bojevanja, imenovano Ninjutsu. Ko mu njegov sensei naroči, naj se vrne v New York in zaščiti orožje, se mora Casey soočiti z nevarnimi japonskimi morilci, ki so odločeni, da se bodo dokopali do orožja in ga izkoristili v zle namene.
Casey, a Westerner studies Ninjitsu in Japan. And in their Master's possession is an Ninja armor with some legendary weapons which goes to a deserving person. Masazuka, another student thinks he is that person but the Master has an affinity for Casey. One day Masazuka attacks Casey and Casey defends himself scarring Masazuka. Masazuka would be banished. He would then become an assassin, who works for a group criminals called The Ring. Masazuka would return demanding the armor but the Master still refuses. The Master tells Casey and his daughter, Namiko to take the armor to America were it can be kept from Masazuka. After killing the Master, Masazuka follows them to Anmerica and tries to get it. Casey is erroneously arrested for crimes committed by Masazuka. He eventually abducts Namiko and demands turn the armor to him. Casey tells him if he wants he'll have to fight him for it.