Hi there
Will look into this more, but according to this blog:
https://ameblo.jp/club-beltempo/entry-12417756022.html
The lower deck of the sightseeing boat is accessible and even has a wheelchair toilet. (The blog is in Japanese but you can paste the URL in Google Translate and it will translate the whole page, or you can just look at the pictures. ?)
The website for the sightseeing boat doesn’t explicitly state anything about accessibility, but it did list a discount for disability ID holders, so the above report is likely accurate – though it would be great if the website stated as such!
There are two different boats, so there could be the possibility only one is accessible…
@ohayotravel do you have any information?