The same thing that would happen to you in Nazi Germany, essentially. You would be arrested, possibly tortured/sent to a camp, and, if serious enough of an offense, executed. The Japanese military (which was the controlling force in Japan at the time when you exclude the emperor) had a special unit set up called the Kempeitai to deal with and quash internal rebellion, for lack of a better term. Their German equivalent was the notorious Gestapo.