Nikko city is located about 125 kilometer north of Tokyo.
[From Narita Airport]
From Narita Airport, Narita Express in JR Line is available for Tokyo station. http://www.jreast.co.jp/e/
From Tokyo area, JR Tohoku Shinkansen, JR Tohoku Line and Tobu Railways are available. Please see below.
As another choice, highway bus is available from Narita Airport to Utsunomiya (JR Station). From Utsunomiya, JR Nikko line is available.
[From Tokyo Area]
Nikko is connected with Tokyo area by Tobu Railways and Japan Railways (JR).
From the terminal station of Tobu Asakusa station in Tokyo to the terminal of Tobu Nikko, it takes 130 minutes by rapid train and 110 minutes by limited express train.
JR Railway and Tobu Railways provide limited express trains connecting directly bewen JR Shibuya or JR Shinjuku and Tobu Nikko station. Please see Tobu or JR web site.
From Tokyo or Ueno Station, JR Tohoku Shinkansen to Utsunomiya station and then JR Nikko Line from Utsunomiya can be available. If you have a good connection at Utsunomiya, the one way trip takes about 100 minutes. If you have a time, you can trip by rapid or express trains in JR Tohoku Line from Ueno to Utsunomiya.
[From Haneda Airport (Tokyo International Airport)]
Take JR monorail from Haneda airport to Hamamatsu-cho and transfer to Tokyo by JR Yamanote Line. Please see above from Tokyo.