Rina Takeda and Hina Tobimatsu co-star as sisters Ayaka and Natsuki Kurenai, the youngest descendants of a legendary Okinawan karate master named Shoujirou Kurenai. As children, they live a happy life with their father (Tatsuya Naka) who encourages them both to practice karate. However, one day a mysterious group breaks into their dojo – killing their father, kidnapping Natsuki, and stealing the black belt which has been passed down in their family for over 200 years. Several years later, Ayaka is living the humble life as an ordinary high school student in Yokohama. One day, when Ayaka was working a group of burglars were stealing a woman's purse. Ayaka uses her karate skills to stop them causing her to be a hero to the public. Ayaka's heroics was caught on camera causing the evil organization to notice Ayaka's fighting skills. Natsuki, on the other hand, has been trained as a killing machine by the mysterious group that kidnapped her all those years ago. Soon, Natsuki and the group begin to take aim at Ayaka. Out of love for her sister and with the teachings of her father still in her heart, Ayaka decides to do whatever it takes to get Natsuki and their family's black belt back from the clutches of the mysterious group.