Here is an article where Paul McMahon walks you through the process of Getting your first programming job in Japan. As you can guess he is not Japanese. He is a developer and he lives in Tokyo so it seems like he knows what he is talking about. Speaking about languages, Paul thinks that:

The greater your technical ability, the less Japanese you’ll need.

and I tend to agree with him - as in any other country, the lower your technical skills are, the lower are your chances that you will be hired if you are a foreigner who doesn't speak the language.

Well covered. There are many small software companies that are unable/afraid to sponsor visas, but need programmers. They usually look for "working Holiday Visa" programmer. Freelancing programmers are less common here, because companies are worried to get things done by them.

This seems to be relevant for remote jobs in Japan. But because it is in Japanese, I cannot say for sure what it is all about.

This is a list of Japanese companies that welcome remote work. The creator welcomes other Japanese companies to add their information, so that the list can grow. Interesting use of GitHub, too.