Born and raised in a family lineage of ninjas serving since the Sengoku period, Kausu and her younger brother Kiriya. After completing their mission and returning home, they found their father attacked by someone and barely alive… Then their father passed away. "I will definitely avenge him with my own hands," the siblings vowed, tracking down and infiltrating the suspected criminal's hideout. They were just one step away from avenging their father! "Sister… I'm sorry…" There stood Kiriya with a knife to his throat… Kausu had no choice but to sacrifice her brother's life…
