I got a JR pass for Green Car for an upcoming trip to Japan. I like to be able to just hop on trains at the last minute without planning ahead or lining up to reserve seats. The guidebooks though say it's essential to reserve seats if traveling in the Green Car.

Is it really necessary to always reserve seats for Green Car for bullet trains and other express trains? I've read that the Green Cars are usually less crowded than regular cars. Can't I just hop on Green Car shortly before departure, take an empty seat, and then move if someone shows up with a reservation? The Shinkansen trains don't even stop very often for new passengers to board.


I think I've been on trains in Europe where some passengers have reserved seats and some don't, if a reserved seat holder shows up, you just move.

Is it some great cultural faux pas in Japan to sit in a reserved seat without a reservation? Will I be arrested, booted from the Green Car, or publicly shamed as an uncouth foreign seat poacher if I don't reserve a seat? Or could I just move to another Green Car seat?

Any advice appreciated.