Born into a ninja lineage during the Warring States period, Kozue and her younger brother Kiraya are unable to save their father when he is suddenly attacked and killed while returning home after a mission. Filled with grief and rage, the siblings vow to avenge his death and begin hunting down the culprit. They uncover the hideout of a suspect believed to be involved and successfully infiltrate it. However, an unexpected turn of events awaits—Kiraya is taken hostage, a blade pressed to his throat, forcing Kozue to make an unbearable choice. To fulfill her father's last wish and save her brother, Kozue confronts the perpetrator head-on, sacrificing everything. A tragic and dramatic tale of vengeance, love, and the unbreakable bond between sister and brother unfolds.