The article, other than the headline, describes a few more details on how kids as young as 6 years old do things different, other the the subway part of it. Public safety doesn't come from fear of repercussions alone, I feel (which probably what 'strong public prosecutors' brings).
Let me guess, you're a conservative who thinks being "tough on crime" is the answer to crime, and being tougher will make us safer.
My dude, Japan isn't particularly tough on crime. It's certainly softer on crime than the US in most ways. In other ways it's tougher on crime that Americans (and especially conservatives) wouldn't accept. For example, they've taken a hard stance on financial crimes, to combat the yakuza. If you're associated with the yakuza they'll cut you off from the finance system. This includes entire businesses. You don't even have to be convicted. A lot of the murder rate in the US is driven by drugs, and that drug money is flowing to legitimate businesses and political contributions.
The reason for the lack of crime in Japan is obviously up for debate, but it's obviously partially social, and also heavily financial. There's less extreme poverty, there's (very cheap) universal healthcare, healthcare for children is free till they're 18, child care is subsidized (and now free for all in Tokyo), transportation is extremely cheap, rent is affordable, food is relative inexpensive, etc.
Poverty levels are way more associated with crime levels than toughness on crime.
The US already does have tough public prosecutors. It also has overly tough mandatory sentencing, poor public defender availability, extremely high plea agreement rates, and folks with a criminal history can't get jobs (and in many cases reasonable housing). We need criminal justice reform, with a focus on reducing recidivism. Our current system basically forces felons back into crime, as they have no alternative to make a living.
This idea that the US isn't tough on crime is mind boggling. The US is tougher than many authoritarian regimes. We have the 5th highest per-capita prisoner population, and the highest total prisoner population in the world. At some point we have to realize that putting more people into prison doesn't solve our problems.
Don't take this the wrong way. I'm not advocating for lighter prison sentences for violent crime, but a small minority of the prison population is violent offenders, and really, a small minority of overall crime is violent and as a whole the rate for violent crime has been on decline since the 70s, with the current rates at a historical low.
Being tough on crime is mostly a political tool, where police departments and prosecutors juke stats and over-prosecute crimes. Again, the vast majority occur through plea agreements, so people don't really get to defend themselves, and they settle because they otherwise face stiffer sentences and can't afford legal representation. This game is for people like you, who vote enthusiastically for people who pretend to solve problems.