The last time I was in Narita, there were fever scanners. It was at a time of an outbreak of some kind of flu. As we were walking to immigration, I saw the signs saying that they were scanning for signs of fever, and if your temperature was elevated, they would pull you aside to make sure you weren't bringing in the flu. Those may be gone now, but if you see them, don't get worried. They didn't pull any one out that I saw. You may be given a form to fill out on the plane with your information, but many countries have now automated that, so you do it at kiosks when you get to the airport. Just follow the others off the plane- there's only one way to go. Then you'll stand in line and show your passport. There may be a few questions as the others have said. Then you walk through the door, and there are carousels where you wait for your luggage. Look for the sign that says Nothing to Declare and go there. You'll probably just walk through the door. If they stop you, they'll look through your luggage, but it's nothing to be worried about.