I've never been Kancho'd, but I've seen it happen. One reason I'm happy that my students are high school aged and above. I will have to say though, a visit to a Japanese police station pales in comparison. If they stop you, not just outside of a bar, but anywhere, they can't ask you to produce ID unless there is reasonable cause that you were involved in a crime. However, if you refuse their "request" they can take you in for "failing to cooperate in an investigation," ostensibly because your refusal means you have something to hide. The charges may not stick, since the obstruction occurred after they made an illegal request, but the fact remains you're hanging out in a Japanese jail with the small likelihood that you'll get out in less than 21 days. The Japanese cops have a crappy arrest percentage for actual crimes of around 50%, but the conviction rate for all crimes is around 99%, and over 90% come from confessions. I'd rather be kancho'd, but that's just me. As a side note, I don't live in Tokyo, and I've only been asked for ID once, and it was a neighborhood cop who just wanted to practice his English. All said, there is little chance you will have any contact with the cops as a tourist, but if you go to Roppongi and party like a rock star, you increase your chances by a lot. There are some interesting threads and articles at
debito.org.