Something about speed limits in Japan, almost no one follows them. I’ve seen police cars go past speeding cameras without their lights on while exceeding the speed limit by ~20% and everyone around them was doing the same.
This sounds like it would be a super dangerous place to drive then, but the speed limits are pretty low on local roads, and instead of driving the speed limit, people drive at a speed more similar to what you’d find for a similar road in most countries.
If you ever have the opportunity to drive in Japan, just drive at a speed you’re comfortable at and not faster than most of the traffic around you, and you’ll be fine. This isn’t legal advice though.
The one place I wouldn’t recommend exceeding the speed limit are those very narrow roads, many accidents happen there, though they’re rarely fatal.
Source: I’m working for a rental car company in Japan