Japan is one of the safest countries in the whole world. With its impressively low crime rate, the worst that most people need to be fearful of is the occasional stolen bicycle or umbrella. First-time visitors might be surprised by residents taking naps on trains with their cellphones in plain sight or by seeing extremely young children walking to school alone. A large part of what contributes to that sense of security is the police force, some 300,000 members strong.