If you access the direct link for the LTE version on the play store, you can add the US version to your cart, and it indicates a 1-2 business days for shipping. However, on the official Japanese Nexus 7 site, it is currently listed as unavailable, though if you choose one of the other versions, you can change that for the LTE version (though the display language switches to English).
North America or European Version
Right now, only the US version is available from the play store in Japan. Both will work in Japan. Neither will grab the NTT Docomo's or KDDI's "800 MHz" bands. This is because there are a ton of bands that are called "800" (even "850" is sometimes called "800").
(Japanese frequency bands)
Docomo's "800" band is Band 19, and KDDI's is Band 18. The EU version supports Band 20, and there is not sufficient overlap on the downlink for this to support Docomo's low frequency (though the uplink does overlap). There is no overlap at all with KDDI at "800 MHz".
So, even though the EU version has "800 MHz" it won't have any benefit in Japan over the US version. This really won't matter at all for Docomo now because they don't seem to have deployed much LTE service on their "800 MHz" band.
North America: LTE Bands 1, 2, 3, 4, 5, 13, 17
Europe: LTE Bands 1, 2, 3, 4, 5, 7, 20
(To display the above information from the official Japanese Nexus 7 site, click 技術仕様, then スペック情報を表示)
Recommended to avoid KDDI
I stand by my earlier claim that the Nexus 7 will suck on KDDI for the immediate future. There are currently problems with Verizon in the US, another CDMA-2000 carrier, who just like KDDI, has rolled out an LTE network. However, the reason for the Verizon suckage is totally different from the reason why KDDI will suck.
[LTE is an evolution of W-CDMA which is in turn an evolution of GSM. CDMA-2000 is based on CDMA. W-CDMA and CDMA-2000 are both "3G" and they are totally different and incompatible technologies.]
Verizon has the proper network to support the Nexus 7, but they refuse to do so, citing the inability to activate a line of service for the device because it lacks a CDMA-2000 radio. If this is true, it's just temporary and mainly an excuse. At activation, the clerk fills out a form on a computer. There is a field for the CDMA radio ID, and if that field is blank, then the the form can't be submitted. Easy to fix — update the activation system.
There are two reasons to avoid KDDI with the Nexus 7 LTE:
- No CDMA-2000 radio in the Nexus 7 LTE, so the device can't fallback to "3G" when LTE is unavailable, which will be...
- All the damn time because KDDI's supported LTE network uses Band 1 (2100 MHz), and they recently got busted misrepresenting the coverage, stating Band 1 covered almost everyone when it in fact covered almost nobody at all.
Nexus 7 as an indicator of unlocked iPhone 5S/C performance with a Docomo Xi SIM
The iPhone 5 technically supported Docomo's Xi network (Band 1, 2100 MHz), but it never really worked. Using an unlocked device with a Docomo contract requires using Mopera as the ISP, as opposed to sp-mode. There has been speculation whether the problems with the Mopera APN were purposely caused by Docomo, Apple, or both.
I think there should be no problems with the iPhone 5S or 5C with a Docomo contract and Mopera as the ISP. I'd speculate that an Apple carrier.plist preference file was denying a connection to Xi with a Docomo (44010) SIM. I could be wrong.
If you can bring an unlocked Nexus 7 LTE to Docomo and use the Mopera ISP with no problems, then it shows that the Docomo is NOT actively preventing non-branded devices from accessing the Xi network.