Un jour, en revenant de faire des courses, Casey est brutalement attaqué par une bande de motocyclistes. Secoué par le traumatisme, le jeune comptable s’inscrit à un programme d’autodéfense où il fait la connaissance de Sensei, un instructeur de karaté charismatique qui le pousse à transformer toutes les facettes de sa personnalité. Casey impressionne par sa détermination et son dévouement, et est invité à prendre part à de mystérieux cours du soir.

Jones is a secret agent who has gone into semi-retirement, concentrating instead on teaching the martial arts to inner city youths. The karate school is run by a kindly old coot named Pops ,played by Scatman Crothers. His gambling debts, however, bring the local thug, Pinky, down on him. To make matters worse, Pinky is then hired by some white thugs who want to get a hold of the property Pops' school occupies so they can build a shopping mall. When things get heavy, Black Belt Jones leaps into action. Only he's not alone. Pops' daughter, Sidney, shows up to lend a hand, proving herself every bit as agile and powerful a martial artist as Jones.

In Okinawa, Ayaka Kurenai was born in the world’s greatest legendary Karate family. When she was a child, her family was attacked by a mysterious gang that seeks legendary black belt. Her father Soujiro Kurenai was killed and her younger sister was taken in front of her. Time has passed. In Yokohama, she was spending her life as a normal high school girl, hiding her real name and her status as a heir of the legendary Karate family. However, one incident brought her a fateful encounter with her sister who was separated in their childhood. But, her sister was raised as a heartless killing machine by the mysterious gang who took her. .