We looked into this quite seriously. But actually - it's hard to do:
1) Equipping a roadbike is not cheap. About $1500 ea is required. So you need at least 30 days rental just to recoup cost of the bike. (Not counting storage, repairs and depreciation)
2) Insurance is a hassle. Premiums for rental of roadbike (that 'may' be taken out of the city costs more than $5,000 /yr)
3) Risk potential. If the bike is stolen, lost, damaged or otherwise requires retrieval or replacement will quickly offset ANY profits gained by riding.
4) Staff Fees. Cost to hire and maintain staff to service the bikes, retreive them, sag the riders, etc. Again very high in Japan.
5) End result - this will work if you are renting at least 10 bikes a day, full time, 300 days a year. Otherwise - its a big money loser. Or you just have a bunch of cheap mama-charis that people will rarely ride more than 5km away and 2hrs or so.
Better choice is to visit a bike shop and see if they have any bikes available for paid demo. This is kinda like renting - but more casual (and generally costs more). Plus there may be some restrictions on where you can ride. And a hefty (usually full MSRP) deposit required.
Best choice is just to bring your own bike and bite the $200 bullet.
If you're flying on Air Canada, it's only $50 each way which is a bargain compared to some of the U.S. airlines. When I did my 3 week tour of Tohoku in the fall of 2010, I even found a hotel in Ueno that stored my bike box while I was away.