Registration is mandatory and registry may be checked on the street if they see you're missing a wheel reflector etc. I'm not sure if that's by local or national ordinance. Japan has a mountain problem, i.e. most of the country consists of them pushing most of the 100-something million people into the two major plains and a handful of other big cities. Where people live in shoe boxes and converge around train busy stations. Where space is doubly at a premium and most cities have no parking zones for bicycles on the streets. If they didn't force people into paid parking arrangements, the streets or more specifically the often conically narrow sidewalks would become impassable with bicycles. I've seen bicycle "tow trucks" in action in Tokyo. It's just a big open truck with an outfit of lock pickers/cutters that impound illegally parked bicycles. The registry helps reunite owners with their bikes and a nice fine. Theft is less of a problem here and depending on the area you'll see bikes that are locked but not locked to anything immovable and people leaving helmets or other items in the basket because chances are nobody will take it.