In Miyazaki prefecture, the most violent in Japan according to [1], the murder rate is 0.9 per 100,000
[1] https://nbakki.hatenablog.com/entry/Murder_Rate_Number_of_Ac...
The major point is that although Tokyo might be "safer" on paper, the risk profile of letting your kid walk around Tokyo vs. letting your kid walk around the city I mentioned is pretty much the same in practice, and this goes for thousands of American cities. There are millions of Americans who could let their kids walk around their community and not have to worry about them being murdered or seriously assaulted.
The safest US city in that respect is Irvine with ~20 per 100k (https://en.wikipedia.org/wiki/List_of_United_States_cities_b...). Irvine is indeed a very safe city, and I doubt parents would be concerned too much with letting their kids walk to school (if only the school was within a walking distance away).
Tokyo reported 224 robberies for 14m residents (https://knowledge.insight-lab.co.jp/tableau/opendata-crime-t...), or ~1.6 per 100k. So 10 times less than Irvine, the place that everyone considers to be basically completely safe.
Now move out of Irvine. Pick a city. San Francisco is ~360, NYC is ~160, Seattle is ~210. Even Mountain View, near Apple, Google, and many other high tech companies is ~60.
And btw, people in Tokyo generally do very little protect themselves from violent crime, since it's so rare. They walk around late, alone, often drunk, paying no attention to their surroundings. I'm pretty sure if people behaved like that in SF, the robbery rate would jump significantly.