Kasumi and her brother, Kiriya, were born and raised in a family that has served as ninjas for generations since the Warring States period. When they return home after completing a mission, they find their father, who has been attacked and barely surviving. ...And then their father never returns. "We will avenge him with our own hands," the siblings are determined to track down the hideout of the man they believe to be the culprit, and succeed in infiltrating. They are just one step away from clearing their father's name! "Sis... I'm sorry..." Kiriya holds a sword to her throat... Kasumi has no choice but to be raped in exchange for her brother's life...