Was Viaweb ever approached by a Japanese company?

Yes, though that description may be stretching the truth a bit; Hiroshi gave up trying to buy us at about the time we decided not to be bought, so it's not clear even to me who rejected who first.

It is true, however, that he got the idea of doing a web-based online store builder plus mall from us, and that what they launched initially was a very literal imitation of our site-- at least on the surface.

I'd be interested in reading this case study and I'm sure others here would. Is it possible to post it here or post a link to it?

Yes, please share it.