Azusa Tsukumo was once a prodigy in the field of chemistry, but after having her research stolen and her career destroyed by a trusted mentor, she now lives a quiet and unhappy life as a high school teacher in the countryside. Her days are spent enduring disrespect from both her students and colleagues, with her only solace being her younger sister, Ruka, who is full of life and lives in Tokyo. One day, Azusa receives a frantic phone call from Ruka, who appears to be in serious trouble with dangerous men. Before Azusa can act, Ruka vanishes without a trace.

Driven by desperation for the only family she has left, Azusa travels to Tokyo to find her sister. Her search leads her to a seedy bar in the city's underworld, where she encounters the yakuza. There she meets Yoroizuka, a ruthless and ambitious lieutenant in a small gang who is also looking for Ruka. In a moment of panic and rage, Azusa uses her forgotten chemistry skills to create and detonate a makeshift bomb, revealing her hidden potential. Recognizing her knowledge as a uniquely powerful weapon, Yoroizuka forces Azusa into an uneasy alliance. He offers to help her find Ruka in exchange for using her chemical expertise to further his own criminal ambitions within the yakuza.

The narrative unfolds as a hardboiled action thriller, following Azusa as she descends into a violent world where money and power are absolute. Her motivation is unwavering, and she is willing to sacrifice her own innocence and morality to save her sister. The story is structured around several key arcs. The first arc introduces the premise as Azusa is dragged into the criminal underworld and forms her dangerous partnership with Yoroizuka. The second arc follows their search for leads, bringing them into conflict with other criminals, including a mentally unstable young assassin hired to eliminate them. In the third arc, Azusa and Yoroizuka finally locate Ruka, who has been hiding on a farm. The sisters are briefly reunited, and the truth behind Ruka's disappearance is revealed: she was the favorite escort of a wealthy businessman named Ryou Ushiko and accidentally witnessed a secret that could start a war between yakuza clans and destroy Ushiko's life. Yoroizuka attempts to use this information to secure his own position, but his plans are derailed when his boss is murdered with a chemical agent. The final arc culminates in a violent gangster saga of revenge and power, as Azusa and Yoroizuka face their enemies in a final confrontation that leads to a bittersweet conclusion.