Kagerou is a kunoichi, or female ninja, of the Kouga clan and one of the ten warriors chosen to represent her family in the deadly blood feud against the Iga clan. She is a young woman of striking and attractive appearance, characterized by her long black hair and purple eyes, and she typically wears a kimono with her hair styled up, often leaving one eye visible. Her most defining trait is her powerful and tragic ability: her breath becomes a lethal poison when she is sexually aroused, a curse passed down to her through her mother’s bloodline. This power makes her sensuality her deadliest weapon, as a single kiss from her is enough to kill a man.

Kagerou’s entire existence is shaped by this poisonous constitution. It prevents her from ever forming a normal physical or emotional bond with anyone, making her a deeply frustrated and jaded individual. Her deepest source of pain is her mad and all-consuming love for her clan leader and cousin, Kouga Gennosuke. Because of her deadly physiology, she is unable to be with him, a reality that fills her with intense envy and bitterness. This resentment is primarily directed at Oboro, the princess of the Iga clan, for whom Gennosuke has genuine romantic feelings. Kagerou is a vocal opponent of the potential peace and marriage between Gennosuke and Oboro, often belittling and criticizing Oboro at every opportunity out of jealousy. Despite her aggressive exterior, her motivations are rooted in a profound personal tragedy: she longs for a love and a future that her very nature denies her.

In the story, Kagerou is a formidable and decisive combatant for the Kouga, though her abilities are as much a liability as a strength. She carries a shikomizue, a sword concealed within her walking cane, and is highly adept at shurikenjutsu, the art of throwing blades. Her poisonous breath gives her a unique and terrifying method of assassination, one she uses without hesitation. Her hatred for Oboro is a key motivator for her actions, and she is among the first to advocate for battle when the truce between the clans is dissolved. Driven by her unrequited love, she even attempts a double suicide with Gennosuke at one point, seeing it as the only way to unite with him, but this effort is thwarted.

Her key relationships are defined by her love for Gennosuke and her rivalry with Oboro. She is Gennosuke’s cousin, and it is suggested that proposals for their engagement had been considered in the past, only to be canceled due to her dangerous constitution. This history only deepens her sense of loss and resentment toward Oboro, who can offer Gennosuke what she cannot. However, her feelings for Gennosuke are genuine and powerful, making her a tragic figure rather than a simple villain.

Kagerou’s development culminates in a final confrontation. Captured and tortured by the Iga ninja Tenzen, who also covets her beauty, she is brought to the brink of death. In a desperate final act, she is used as bait to lure Gennosuke. When he arrives, she attempts one last time to kill Oboro in a fit of mad jealousy after realizing Gennosuke will never go through with it himself. However, in a tragic turn of fate, Oboro uses her own unique eye technique to reverse Kagerou’s deadly power, turning her own poisonous breath back upon her and causing her death. Her end is a direct result of her own poisoned nature and the consuming jealousy that defined her life.