As you know, Japan is safe. In many places it is safe to walk alone by a woman at night, and we often see the sight going to school or going out alone for children around 10 years old. Even if you sit down on a train seat and sleep, you are OK in most cases.
Although the incidence of crime is relatively small, violent people, anti-social impulses and propensity are also in Japan. The other day, a young man arrested. He murdered 9 people in a short beriod.
Japan is peaceful, but please be careful not to overrepair even if you come to Japan.