Rina’s work is dangerous. Last winter, a suspect pulled a box cutter during an arrest; an agent took a slash to the forearm. Another man, upon being caught, began screaming that Rina was a “fake woman” and “entrapping” him—a common counter-accusation.

Yet Japanese courts have grown less tolerant. Under a 2017 legal revision, chikan convictions can carry up to seven years in prison, and increasingly, judges are ordering mandatory counseling. Rina’s team also works with railway companies to install more security cameras and women-only cars—though she notes that gropers simply migrate to mixed cars during less monitored hours.

Once a target victim (often a high school or university student) is identified, Rina executes a "shadow lock." She moves within 18 inches of the victim, pretending to read a manga on her phone. At this range, she can hear the change in the victim’s breathing—the sharp, panicked gasp that signals the exact moment groping begins.

This is the critical moment. Unlike a police officer who waits for the crime to happen, Rina intervenes at the preparatory stage.

As the train approaches the next station, she uses her left hand to drop her keychain—a loud, metallic clatter. Distraction number one. Then, she turns to the victim and says loudly in Japanese: "Mari? Is that you? Oh my god, we haven't seen each other since high school!"

This "stranger rescue dialogue" serves two purposes. First, it forces the perpetrator to break contact reflexively (sudden social noise triggers the freeze response). Second, it gives the victim a role to play. In nine out of ten cases, the victim immediately plays along.