Gambling in Japan is a curious mix of strict laws and surprising exceptions....

https://wiki-tonic.win/index.php/Is_Horse_Racing_the_Biggest_Betting_Sport_in_Japan%3F

Gambling in Japan is a curious mix of strict laws and surprising exceptions. While most forms remain illegal, you’ll find popular legal outlets like pachinko parlours, horse racing, keirin cycling, and motorboat racing (kyōtei)