The direct bus from Narita Airport or Haneda Airport to the Nikko & area is called the Airport Liner Marronnier.
Price is not covered with any regional bus or train pass. Takes about 2 1/2 hours.
Once a day it goes and comes here to Nikko, most likely you will need to get the bus at JR Utsunomiya (宇都宮駅発 ) station, west exit, turn left;
From Narita, the bus will take you to JR Utsunomiya station and here is where you catch the JR Nikko line. Be careful, not every train on the JR Nikko line goes to Nikko; some stop at JR Kanuma!
Taking this bus is a great way to save your JR Rail train pass until AFTER spending two or three days in Nikko.
On the flip side, Nikko is a great place to spend you last days in Japan as you can take the bus direct to the airport with less effort than the all the transfers of trains through Tokyo. The ticket office in Utunomiya is on the west side, left when exiting the station.
Nikko is bigger than nearly every travel guide suggests. For example, you will need to buy a separate bus ticket to get to Senjogahara, Kegon Falls, Yumoto Onsen, Mt. Nantai.