Narita can be an extremely busy airport. If you are flying tourist (coach) class, you ought to get back to the airport a couple of hours before departure time. (They say three or four, but this is not necessary. If you are delayed at any stage of the process you will be whisked on through.) After going through security screening, the next long wait is for Immigration. Again, bring a book or magazine (or a couple of cans of beer). If you are delayed and in danger of delaying the flight, they will look for you and zoom you on through, so don't worry too much. (This is because if they don't find you, they must find your checked bags and remove them from the plane. Unless you are dead or an actual terrorist who has flown the coop, finding you is generally the easier task. So, go ahead and have another six dollar beer.)