Aya, a female ninja of the Mizutori-ryu ninjutsu, has left her life as a ninja behind and now teaches self-defense at a dojo in the city. However, as the dojo struggles financially, she is forced to participate in an underground fighting tournament. At that moment, her former agent comrade, Oomae Daiichi, appears and persuades her to rejoin the organization to uncover the truth behind Jinzai Onizuka, a dictator who wields power over Takishima—a lawless island near the border. Answering his call, Aya enters Onizuka's fighting tournament, but her identity is exposed, resulting in a crushing defeat and a humiliating downfall!