I see.
I just tried using Rakuten Travel's Jpn site via Google Translate. It doesn't seem to work well. It translates the initial page fine for the most part, except some of the pull-down menus do not get translated. Then you do a search, and it fails to translate the search results page. Perhaps I'm using it incorrectly. It'd be nice if there was a way for non-Japanese to access rates and packages offered on Rakuten's Jpn website.

So, to summarize options for non-Japanese visitors looking to book rental cars in Jpn, are these the only English options?
- Tococo (which requires pre-payment)
- Tabirai
- Look for individual rental agencies with English websites
- Toyota Rent-a-car (and possibly others), which offers phone# for English booking

Not being familiar with Tococo or Tabirai... is Tococo like Expedia/Priceline (ie, vendors that you make payment to), and then Tabirai is like Rakuten (ie, aggregator / search engine that you can also book through, but the actual booking and payment are with hotels/operators)?