Kasumi and his younger brother Kiriya were born and raised in a family that has served as ninjas for generations since the Sengoku period.Waiting for them when they return home after completing their mission is the father of Insect Breath, who has been attacked by someone. ...and his father passed away. "I will definitely avenge my enemies with my own hands", the brother and sister's tenacity succeeded in finding and infiltrating the hiding place of the man who seems to be the criminal.One more step to clear my father's regrets! "Sister... I'm sorry..." There is the figure of Kiriya with a sword pointed at his throat...Kasumi had no choice but to be raped in exchange for her brother's life...