Teruko Nakazawa once intervened in a knife fight between an ex-offender and their mother — all in a day's unpaid work for Japan's army of volunteer probation officers.

The 83-year-old, who jokes she is a "punk" as she puffs on a cigarette, devoted decades to supervising and helping rehabilitate convicted criminals on parole.

But she did not take a single yen for her hard work under a long-running but little-known state plan that some say contributes to the nation's famously low crime rate.