No, Japanese can invest in other markets using international brokers. I don't know details on the fees and currency conversions. Investing in a foreign exchange is always at a slight disadvantage because of currency conversions and fees.
US stocks are traded on foreign exchanges. Even if you insist on buying on a US exchange, the currency conversion is not very expensive. If you're a buy and hold investor, it won't matter at all.
For a US centric view: https://www.investopedia.com/articles/investing/032615/how-t...