Sounds like an interesting trip! I spent 2.5 weeks in Tokyo for business in 2000, and I did not see people riding bicycles on sidewalks. I saw LOTS of bicycles on the roads and parked everywhere. Lots of workers commuting to their jobs via bikes, which I thought was great. My manager and I walked to work every day. It may depend on the part of the city, but it appeared bike friendly to me. That said, I would not want to bother taking my own bike unless I had a folder that could pack in its own suitcase, like a Bike Friday (which I just happen to have

). For me, it would not be worth the hassle, risk, or extra cost to pack a non-folding bike unless I were traveling abroad for months.
Have fun!