Like many things in Japan: the Japanese police are a riddle wrapped in a mystery inside an enigma (Winston Churchill's famous word's about Russia).
Japanese police are amongst the most militant police forces in the world. However, on an individual basis most of them are perfectly friendly. As departments they go out of their way to maintain a good public image.
Few people in Japan live in fear of the police. It's quite common to pop into a police station to ask for directions. The most likely time to run into the police: when you're on your bicycle.
People in Japan are so law abiding that the police tend to focus on bicycle related crimes.
Even rickshaws get some police attention.
It's common for police to let bicyclists off with a warning.
In the case of parking violations: towing is common. However, it's a fair system. You can pay to get your bicycle back. They even check if the bicycles are stolen and try to return they to their original owner (they're never stolen).