This video is a bit misleading. Very few kids here in Japan travel completely alone to school unless they live in very rural areas (and even then, they probably go with older siblings). As you see later in the clip, most kids go to school together with friends in small groups, at a minimum a pair but sometimes in huge groups. In my neighborhood, at around 8:45 in the morning, you can see virtually the entire local elementary school walking together towards the public school. They might not be under direct adult supervision, but they are rarely alone and there is always an adult nearby because people are usually commuting to work on the same roads/trains that the kids are using to get to school.

And like they said, the reason this can happen is that violent crimes against children such as kidnapping are almost non-existent here. Adults are far more likely to end up missing/dead here. Contrast that with Western countries like the U.S. or Australia and it quickly becomes apparent why people are escorting or bussing their kids to school in those countries.

I will say that there is a negative side to the "independence" they are touting in this video, which is that these same children often run completely free after school with zero adult supervision. Some of them can get a little wild (throwing rocks at passing cars and stuff or making way too much noise in a crowded residential area) but the cultural attitude here is that it's just "kids being kids," although I sometimes suspect that's code for "we don't want to actually have to parent our kids unless someone forces us to."