Daisuke Jigen, the sharp-shooting partner of Arsène Lupin III, finds himself on a rare solo mission driven by an unusual problem: his trusty Smith & Wesson Combat Magnum feels off. The gun’s accuracy is failing, a potentially fatal flaw for a man whose life depends on his draw. Convinced he needs the help of the world’s greatest gunsmith, he returns to Japan after a long absence, following rumors to the decrepit and lawless district of Deigyo-gai.

There, he discovers the renowned gunsmith is not a hardened criminal but an elderly woman named Chiharu Yaguchi, who runs a small watch repair shop as a front for her real business. Jigen’s simple repair job becomes complicated when he meets Ito, a mysterious young girl who comes to Chiharu seeking a gun of her own. She is being hunted by a ruthless organization led by Adel, a terrifying and disfigured crime boss who has lost a leg and her voice but none of her cruelty. The organization has been using children as human guinea pigs in horrific experiments, and Ito is a survivor they are desperate to reclaim.

Despite his gruff, lone-wolf nature and his admitted dislike for children, Jigen finds himself unable to walk away. When Ito is kidnapped by Adel’s forces, Jigen launches a desperate, one-man war against the criminal empire. The narrative follows his journey from a pragmatic gunman fixing his tool to a reluctant protector, forcing him to confront a far more personal battle than he anticipated. The setting is a stark, rain-slicked underworld far removed from the glamorous heists of Lupin, depicting a gritty urban battlefield where Jigen must rely solely on his legendary speed and cunning to save the girl and destroy the organization hunting her. This mission peels back the character’s stoic exterior, revealing a more vulnerable and surprisingly sentimental side as he learns to connect with the orphaned Ito.