This may be painfully obvious once you think about it, but for those who haven't, here's a way to get around the Xbox 360 country lock for downloadable content. Microsoft's chosen to disable certain game demos and game videos for people of certain regions, but we want all our media to be free, don't we?
Go online to xbox.com and register a new gamertag with an email address not associated with any previous account. Then make sure you set your country to either Japan or America—perhaps making one tag for each. Then when that's done, go on your Xbox 360 and choose "recover gamertag" to grab the info from this tag onto your 360. Now you can see all the Japanese games you've been missing out on.