Using foreign prediction markets from Japan?

There was a post a year ago https://www.reddit.com/r/JapanFinance/comments/1f6dnqm/the_legality_of_prediction_markets_in_japan/ and I'm wondering if anything has changed.

I'd like to put a small amount of money in prediction markets for fun. I'm obviously happy to be taxed on any gains. Is there anything I should be aware of before starting?

Note: I'm also American if that matters.

by litte_improvements