For the journey back to narita airport, should i make an advance reservation?Yes, unless you do not know your exact date and time of departure yet.
i'll be returning to tokyo via tohoku shinkansen, so would it be advisable to make the return shinkansen (sendai to tokyo) and the NEX reservation (tokyo to narita apt) in advance?:)
Yes.
Would it be a problem to just "hop on and off" the shinkansen and nex as Dave says?:)
If the shinkansen has dars with unreserved cars, you can just hop on with your Japan Rail Pass and use the unreserved seats. However, if you want to use reserved seating, a seat reservation is required in advance. Japan Rail Pass regulations state that the seat reservations have to be made before boarding the train.
Note that the Narita Express and the fastest shinkansen between Sendai and Tokyo (Hayate and Komachi) do not carry unreserved seating. The slightly slower Yamabiko trains between Sendai and Tokyo do.
Just as an aside, I'm not planning on reserving my shinkansen ticket from tokyo to sendai, just thought i'd "hop on" hehe, but is that really ok?:)
If you use unreserved seating on a Yamabiko train, yes. But if you want to use a Hayate train, Komachi train or reserved seating on a Yamabiko train, you must make seat reservations in advance and cannot just hop on.
