One of the stranger things in Japan is that when the police cars are patrolling, they’ll have their lights on, flashing.
In the U.S. that would mean they want you to pull over, hand them your license and registration, and then probably get a ticket.
But over here, they are simply making their rounds and showing their presence. And sometimes they’ll have little check tests for the biking people in the area; are you on the correct side of the road, do you have a second person on your bike’s back seat, are you biking side by side, etc.
So when you see the car flashing behind you with police markings, don’t frantically pull over to the side. Just ignore it.
(when they start the sirens, however, feel free to pull over and get out of the way) 🙂