This rental wheelchair may be fitting to your requests. You can get it in Tokyo, and keep it continuously all through your trip, and return it in Tokyo when you will leave.

https://odekakeoffice.jp/en/rental/

We are frightened by news coming from Japan about heavy rain and floodings, is this common each summer ? Everywhere ? Or just this year ? Is is this buzz from journalists ? Is there any real risk (with an electric wheelchair)?

Scroll down to where 123Eileen comments on the cost and how to find out about them.