Jailed a few months in Japan, but still a good guy

Hello fellow redditors!

Been told that you don’t end up in prison in Japan for menial things, but once there it’s hard.

For research purposes, I need to find a reason for a man to be jailed for a few months, but without him being such a bad guy.

I thought he (30-40 man) could have broken the law for a good cause, not a blood crime. I don’t know if white collar misconduct could be enough. Something that still makes his family and friends turn their back on him. But maybe in Japan bringing shame by getting caught and jailed is enough regardless of what it is about.

If possible, I’d like something that add a local touch, not a generic reason that is valid anywhere in the world.

Thanks for your help!

Edit: well, I wasn’t sure if it would be the right place to ask, but I thought at least there would be knowledgeable people kind enough to help 😊