I think @wanping may be able to help as well

Maybe @wanping knows a bit more, but according to this you can watch the yumomi in a wheelchair:

https://www.kusatsu-onsen.ne.jp/netsunoyu/0001.html

Not a lot of detail! So might want to contact them directly.

This blog also mentions going and there were no steps and the staff were kind.

https://www.z-z.jp/thbbs.cgi?id=kokofurig&p3=&th=119

I think @wanping or @tak can help you!

There are accessible rental options, but not at every rental location. A common lift-equipped van is the Toyota Hi-Ace, but there are mini-van options with ramps in the back – just be sure to measure and be sure your husband can fit in. I use an Invacare power wheelchair and can get in some if I recline my backrest. If we are going to do…

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There are a few other travel agents dealing with accessible travel like @ohayotravel and @wanping