a VirtualTourist member
I find the trains in Japan to be very confusing. I have found an English schedule link online, but it seems to have all the names wrong. Does anyone know (have heard of) the "Nasuno line" that runs between Saitama and Utsunomiya? I think it's the "Bullet" train, but I'm not sure. Also, there is (according to my link) a train that covers 80KM in 12 minutes. Is that for real?
Nasuno is a bullet train (Shinkansen) that runs on the Tohoku Shinkansen Line. It is a "local" train that stops at all stops on the Tohoku Shinkansen Line. Unless you have a JR Pass, you shouldn't bother taking this.
In order to give you the best advice, where are you staying? It can make a big difference on how to get there. Hyperdia is the best option to find out how to get to Nikko, however there are two services that are easy.
The Tobu Spacia trains are the easiest. They go directly from Shinjuku to Nikko. TOBU Nikko Station is next to Nikko Station. You can also take trains from Asakusa or Kita-senju, but there is a different train that I can't find information in English.
For regular services (without paying for a reserved seat), here are your options.
Shibuya/Shinjuku/Ikebukuro: Take the Saikyo/Shonan-Shinjuku Line to Utsunomiya. The confusing part is knowing which train you will take. The Shonan-Shinjuku will take you all the way there, but the Saikyo will require a change around Akabane Station to the Utsunomiya Line. (Just an FYI, the Shonan-Shinjuku Line is actually 3 lines combined into 1. The Utsunomiya, Saikyo, and another one south of Tokyo.) Then change to the Nikko Line in Utsunomiya.
East side: Go to either Kita-Senju or Asakusa Station. At Asakusa Station, go to the Tobu trains, not JR as the Tobu train is a private commuter train line. Then take a train to Tobu Nikko Station. There are a few options but there is a direct train. Others require you to change as trains don't always go where you want them to.
When searching Hyperdia, be sure to use "Asakusa (Tobu)" and "Tobunikko" when doing the search on the east side. Be sure to make it to the train you want by being early.