Originally Posted by
ninja138
....The only segment you can reserve with the JR rail pass online is the Dec. 31st N'Ex from Narita to Tokyo. All others will need to wait until after you arrive (and little chance that you will get the reservations).
I don't believe you can reserve even that segment in advance online (for all practical purposes). Last time I checked, if you use the online reservation feature offered by JR East you have to pick up the tickets in person at a JR ticket office by 9pm of the night BEFORE you want to travel.