[Snorkledorf]

The hardware for PWs bought in Japan is (aside from the Wi-Fi) identical to e.g. the US ones. It's actually the individual books that control the direction of text flow, kinda neat! (For reference and light reading horizontal text -- paged left-to-right -- is fine, but for long-form reading it'll drive you nuts.)

When a PW opens a properly-formatted Japanese book (i.e. purchased from Amazon Japan) the text flows vertically and to the left, and the tap zones are automatically flipped left-for-right so everything flows naturally. The "page forward" area on the left is larger than the right area and all that.

All the Amazon Japan books I've seen so far have been AZW3 files using CSS to make the text flow vertically, but I haven't yet looked into what voodoo they use to alert the hardware to flip the tap zones. Nor have I encountered any AZW/mobi files at all from the Japanese Kindle store, now that I think about it. They probably don't have the layout flexibility...