Searching for directions from 35.443708,139.638026 to 35.689487,139.691706 yields results on Google Maps, however this query to the directions API does not:
Anyone have any ideas? It seems to be specific to Japan. You'll want to update the departure_time above to now if you're actually testing this.
I've filed this bug with Google, I'd rather find out it's something wrong with my query though: http://code.google.com/p/gmaps-api-issues/issues/detail?id=4498
Thanks for your help!