Originally Posted by AlwaysAisle

Alright, maybe this will clarify…

On JR trains in Japan, “reservation” = “buying ticket”

Reservation required means you need to purchase a ticket with the train number specified with specific seat assignment. This can only be done in Japan, cannot purchase JR train tickets while you are still in the U.S.

Once you arrived at NRT, you can purchase the ticket at JR Narita Airport station at the airport. Once you purchased the ticket with specific train number and specific seat assignment, then you have made the “reservation” for the train. Ticket sales for JR trains will start from one month before the trip. So the day of arrival at NRT, you can “reserve” or purchase the ticket for return portion from Tokyo to Narita Airport at same time at JR Narita Airport station.

Does this clarify any confusions you had regarding JR trains?