Gambling in Japan is a curious blend of strict laws and curious loopholes....

https://varimail.com/articles/what-is-the-best-first-legal-bet-in-japan-for-a-newbie/

Gambling in Japan is a curious blend of strict laws and curious loopholes. While most betting is illegal, you’ll find popular exceptions like pachinko parlours, horse racing, keirin cycling, and boat racing known as kyoutei