The Niigata line car ferry 2nd class and the Naoetsu line express car ferry 2nd class have different rules, so please be careful.
Niigata Line Car Ferry 2nd Class:
Reservation is not needed if using only 2nd class on the car ferry. The car ferry 2nd class is a large carpeted area with no assigned seating. Please purchase your passenger tickets at the ticket counter of the given port on the day of departure. However, if you are boarding with a vehicle or with a group of 15 or more people, then you must make a reservation even for 2nd class passage.
Naoetsu Line Express Car Ferry 2nd Class:
The express car ferry 2nd class has entirely assigned seating and requires prior reservation. However, when the car ferry is undergoing maintenance and the express car ferry is commissioned for the Niigata line, 2nd class will have unassigned seating.