Welcome aboard Timothy!
You will find there are many paths besides real estate to passive income. If you have a particular yearning for real estate, then by all means go for it! There is a wealth of real estate entrepeneurs on this site and any of them are more than willing to help you along the way.
You find yourself in a unique situation being in Japan. You have ready access to resources most people in the US would never try to get. Look around at the things the Japanese use that Americans do not. There is an opportunity for you to introduce those products to the US market.
You also have a chance to visit and develop relationships with Japanese factories. Look for Japanese goods sold in the US that could benefit from a facelift or some tweek to improve the product. There are people in Japan that desperately want to penetrate the US market. You can help them do that for them.