Travelers and agents often ask about the difference between Ordinary (coach) and Green (first class) cars.
The following are some basics.
1. Reserved seats are available in both classes on long-distance trains. Green Cars are reserved only, while Ordinary class has both reserved and non-reserved cars. With Japan Rail Pass reserved seats are available without charge in the appropriate class.
2. Green Cars do offer wider seats, more leg room and more luggage space, but the difference in comfort is not as extreme as with many airlines. Green Cars may have small amenities like tea or hot towel service but there are no special meals served. In general, passengers who wish to use Ordinary will not find it uncomfortable.
3. To upgrade from Ordinary to Green on individual trains when using a Japan Rail Pass the passenger must pay not only the Green Surcharge but also the Express Surcharge which thus becomes a kind of ‘penalty’. Such upgrading is generally not recommended.
4. Some trains, such as the Railstar service between Osaka and Hakata, or the new Kyushu Shinkansen offer only Ordinary seating which is somewhat roomier than the usual Ordinary seats.
information provide by JNTO (NY): 5/30/2008