@Kyohei Nakata Welcome to Microsoft Q&A forum!
From the Feedback Channel Improvement of map data for Japan, Our Product Team confirmed that, support for Japan is being investigated as a future addition. In the mean time, Bing Maps can be used for Japan. Please review the options available at Microsoft.com/maps.
Also, I would suggest you, please provide your feedback and upvote on the feedback request.
If an answer is helpful, please click on or upvote
which might help other community members reading this thread.