no worries really. I haven't seen any crime or heard of any since I've been in Japan. Maybe I'm just lucky but I think it's just that it's that low. I feel safe everywhere I go and at all hours. Even at 3 am you could see old women walking dark alleyways home or to wherever they were going. And not just old ladies but everyone. You just don't feel unsafe anywhere.
The people are very respectfull, so all you have to do is enjoy the vacation and have fun.